Seven days later, as hope faded she would be found alive, she was spotted in remote bushland west of Canberra. Emergency responders first thought they'd found a body - until she raised her hand.

Almost three years on, Kat is for the first time sharing her story of survival. She hopes it will convince others their battles are worth fighting.

For most of her life, Kat could light up any room. But after being diagnosed with clinical depression the year before, the 19-year-old was struggling to cope.

She had increasingly been turning to alcohol and drugs to drown the dark feelings she felt were taking over.

It was about 11am on Saturday, September 5 when Kat's parents, Ronnie and Rowena reported her missing after receiving the alarming message.

Initially, police gathered telecommunications data, described as “inherently unreliable", and without much else, set off on foot to search for any sign of Kat in an indistinct area west of Black Mountain Tower.

Less than 24 hours later, Detective Sergeant John Giles, a team leader with criminal investigations, stepped in. He knew Kat had spoken of self-harm in the past.

"She sent a text message to her mum and dad that caused me all sorts of concerns," Giles said.

For days the 19 year old he was searching for hadn’t accessed social media or bank accounts, hadn’t used her mobile phone, and hadn’t contacted friends or family. There was no sign of Kat, her car or her phone. Without those, Giles' team had almost nothing to go on.

Late on Sunday night, ACT Policing search and rescue mission coordinators senior constable Lachlan Ryan and federal agent Mark Travers were consulted. Traditionally, to bring in the search and rescue teams police not only need a missing person but they need a last known point.

"It’s from that last known point that we start our planning," Ryan said. "We needed to find the vehicle, or some evidence of where Kat was."

Mobile phone information established that her phone had been located by three towers, Fadden, Isaacs Ridge and Black Mountain before signal was lost about 11am on Saturday. Initially it was baffling, but this information would prove crucial.

"The search area was huge, but that was all we had," Ryan said. "So we started searching, boots on the ground."

In addition to the search of bushland, police searched a two-kilometre radius from where Kat was last seen, and continued on over the coming nights to search for Kat's little black Hyundai in every car park in Canberra - from shopping malls to hotels. When nothing eventuated, they searched whole suburbs in search of the car.

On day three, police released a public message to ensure the whole of the ACT was on the lookout. That decision was particularly tough on the family. Kat's mum Rowena feared if Kat really just didn't want to come home, distributing the information and images of her to the media could have had the opposite effect they intended.

"Part of us was hoping she was all OK and she just didn't want to come home. So seeing her face everywhere, we were also thinking she might not like that," Rowena said.

ACT Policing's David Packwood had been called in as media liaison. He told the family he would hold their hand throughout the ordeal if they put their trust in him.

One morning at 6am, Ronnie called Packwood asking for help. Television camera crews were camped on their front lawn. Reporters were knocking at the door trying to get footage.

Packwood, who has a daughter the same age as Kat, rushed to their home. He threatened to have the crews arrested if they stepped foot on the private property again.

Throughout the ordeal, he helped manage a barrage of media requests and true to his word, stayed close to the family.

By the afternoon of day three, police knew time was against them. Clutching at straws, they theorised about what had happened.

They came up with five most likely scenarios.

Scenario one: She had deliberately gone off the grid. Scenario two: she had crashed her car in the ACT rural area. Three: someone else was involved in her disappearance. Four: She'd confided her whereabouts or plans to friends and they were helping her avoid being located. Five: She’d left the ACT and was interstate.

Police went back through the information they’d already gathered.

"The most plausible scenario to us was that Kat had crashed her car," Giles decided.

Kat's father, Ronnie, recalled the discussion he had with Giles at the time.

"John Giles really had a hunch, he had a hunch from the start. We clung to that."

If this was the case, other factors were considered that gave both Ronnie and Giles hope.

"She was never a fast driver, her driver experience was limited, the vehicle had safety features," Giles reckoned.

He pinned his hopes on the car's safety features protecting her.

"We stood the investigation up on the scenario that she had crashed and she was alive. Three days had passed, time was against us if the evaluation was correct."

But the clock was ticking, and police knew it.

By day four, Giles asked himself what his expectations of the search would be, thinking about his daughter.

"Even when I was away from work during those six days, I never slept. Thank god I was surrounded by a team of people who shared our belief and were just as heavily involved as I was.

"I took it very personally and put myself in her dad's shoes.

"I rang Ronnie every day and let him know what was happening, where we were.

"On day five, I dreaded making the call. I could hear the anticipation in his voice as soon as he would answer, always the expectation that I would tell him where his daughter was."

As despair was setting in, a glimmer of hope arrived.

On day five, ACT Policing Intelligence was getting new information on the mobile phone investigation.

"Initially we were told it could extend to eight kilometres west of Black Mountain Tower. They updated that to say it could be 80 kilometres from any of the cell towers. That introduced a massive new area."

Six days after the search began, Giles was asked to consider if Kat had died and they were, effectively, searching for a body.

"It was a call I didn’t want to receive. It was having an impact on ACT Policing resourcing and I was told consideration should be given to downgrading the search."

But when Ronnie asked if he thought his daughter was still alive, Giles reassured him.

"We wouldn’t have resourced this at the level that we were if we had no hope."

Despite evidence mounting to the contrary, the niggling idea that Kat was still alive was gnawing at Giles.

"I called my mum that night, asking what I was missing. She says she didn’t know what I was talking about, but knew that I would work it out."

"It was really stressful. I had another sleepless night."

Then came a breakthrough. Behind the scenes, police intelligence team member Amanda Rankin was liaising with Vodafone and data specialists.

A specialist suggested the earlier interpretation of cell data could have been misleading. He said if the towers located the phone at about the same time and there was an arc of coverage coming from them, the focus area could be reduced by concentrating on where they overlapped.

The specialist overlaid the data onto a map, which highlighted two distinct smaller areas.

"That night, we went back and changed all our planning. We started at 6am the next morning. There were two distinct areas at the Cotter," senior constable Ryan said.

On day seven, Giles was directed to take the day off. But bound to the case, at 7am he arrived at the staging area in his trackies and T-shirt.

It was about 9am when he got the call.

A vehicle, upside down and badly damaged, had been spotted in a gully. Hearing the news, the family braced.

"I was the first one down to the car and I expected the worst," Giles said.

But Kat wasn’t there.

"I moved the car around a bit, almost expecting her to be underneath it and she wasn't," Giles said.

The call was made to wait, nobody was to search for Kat until the tracking dogs arrived.

Waiting for the go-ahead, ACT Parks Murrumbidgee area manager Tim Chaseling stood on the road above the wreckage.

As he looked across to the opposite side of the hill, something caught his eye.

Out of the scrub, a hand raised.

"We were like, 'bloody hell, I think that's her'".

Chaseling started running. Down the rocky, steep gully and up the scrubby other side.

He found Kat, her fragile body lying in the scrub, head covered in dried blood, eyes sunken from dehydration and face weathered from exposure. She had glass embedded in her neck from the crash, and her ankle was badly broken.

Giles, who hadn't seen the hand but heard the commotion, thought he was looking at a body.

Then, he heard a small voice: "Excuse me, can you help me? I'm stuck."

Kat's Hyundai had crashed down a steep embankment in remote bushland. It couldn't be seen from the private road above. A search helicopter travelled near to but never over the area.

Incredibly, Kat had crawled up the steep bank on the opposite side to the road, thinking she was heading for safety when in fact she was going further from it.

Kat barely remembers her time in the bush, something put down to trauma-related memory loss. She remembers being in pain for a time, not knowing where or how or why.

Her next memory is of holding the hand of an SES volunteer, and then being wheeled into hospital calling for her mum.

"I don’t even know when I woke up," she says.

"I just remember being there [in the bush]. I don't remember where I went or why I chose that place. I don't know how I planned it, I don't know how I found it. I haven't been there before."

Kat and police think she got knocked out during the crash, and could have been in the car for a few days before somehow finding her way out of the wreckage.

"I think I vaguely remember hearing things, hearing people, hearing voices, or seeing blurry stuff. I don't remember completely. I just started yelling 'help, help, help' and then they came.

Her family simply call it a miracle.

Ronnie says he's never yelled as loud as he did when Detective Sergeant Giles phoned him to say they'd found his daughter.

"I was just screaming," he grins, tears welling in his eyes.

"We never gave up, we never really lost hope. It was just our faith that kept us really going. Plus the support from all of our friends, and the community," he says.

Ronnie says the feeling of knowing your child is missing is indescribable.

"It's something no parent should ever have to go through."

Rowena called her sister in America immediately on hearing the news and instead of words, all she could do was cry into the phone.

"My sister was like, is she alive? Is Kat ok?" Rowena says.

In the intervening years, Rowena says her youngest daughter has become stronger.

"We keep on telling her she's more than enough, that she's the bestest. She's such an amazing person. We're here to support her as much as we can, and I hope she knows that."

Kat's sister Megan says the hardest part of Kat being missing was the feeling that she hadn't been there for her when she needed it the most.

But she admitted it's not always easy to support loved ones with mental illness.

"I didn't fully understand it and I don't fully understand it, so it's difficult to support someone through that," Megan says.

"We had never been that close, so I was not feeling like a good sister when she was gone, I was thinking if I would ever get the chance to make that up.

"I honestly feel like it was a miracle that she was found."

Since that time, Megan's learnt to be as understanding as she can.

"Even though you don't understand, still being there for them, regardless of what's going on. That's what matters."

Kat knows she was severely depressed before she got in the car. She hopes her story will encourage others to seek help before it's too late.

She can't stand the thought of ever putting her family through something like it again.

"The whole point of this is for me to survive that, and if my story can save one other person’s life, that's enough for me."

"Maybe I let my depression cloud over the fact that I actually had such desire and will and want to actually live.

"The way that depression works is that it consumes you completely. Even if I've got bits of hope in me, it will still be my depression trying to crush that, but [the will to live is] there obviously because I'm still here, and I got through that."

In sharing her story, Kat hopes to reduce the stigma that others face when talking about mental illness. She hopes it will encourage others to speak up.

She wants others to know that suicide is not an answer.

"Talk to your friends, talk to your family. Don't be ashamed, and in turn don't judge," she says.

"You are not your mental illness, you are so much more than that."

She's forever grateful to the emergency responders who saved her life.

"The work they do each and every day betters this world in more ways than one. Not all heroes wear capes, and they are my real heroes."

Kat has postponed university and, with her boyfriend Nik Kaleb, has since travelled to different parts of the world. She works full-time in hospitality, which she says was difficult to go back to when plenty of people recognised her face from the media.

But while she still struggles with depression, she's learning to cope.

"Having something to look forward to is always a good thing. I'm exercising, actually taking my medication. And surrounding myself with good people, people that actually care about my wellbeing and support me."

"I'm extremely lucky to be alive. Extremely lucky.

"I want anyone else who is suffering from this to realise, before it's too late that there is actually something worth living for. That your battles are worth fighting."

Lifeline: 13 11 14

Beyond Blue: 1300 22 4636