The 25-year-old picnic rider died at the scene 21 kilometres southeast of Junee, when the car her partner Garry Kirkup was driving hit a tree and burst into flames.

Kirkup, who trains horses at Thoroughbred Park in Canberra and who had a runner at Flemington on Oaks Day last month, was airlifted to the capital with serious abdominal injuries.

He's since been cleared of serious head and spinal damage but had an operation on Sunday, and was still in an induced coma late on Monday with doctors having delayed further surgery until Tuesday.

Johnson's death comes just nine months after her close friend, 22-year-old Riharna Thomson, died from serious head injuries sustained in a trackwork accident at Thoroughbred Park.

The Canberra racing community was left stunned by its latest tragedy, and jockey Carly Frater-Hill stood herself down from riding at the Sapphire Coast on Monday.

"Samara, she was awesome, she was such a happy person, always smiling, she loved life, loved people," Canberra's group 1-winning trainer Nick Olive said.

"She just loved being around the horses, everyone said gidday to her. She was a really nice girl."

Olive was one of several trainers in Canberra who Johnson rode trackwork for. She was an accomplished jockey at the picnics, and her last winner came on October 7 when she rode Liabilityadjuster to victory in the Young Cup.

She won the Boorowa Picnic Cup and the Tomingley Picnic Cup this year. All up she rode 48 winners, enjoying her best season in 2015-16 when she produced 21 winners and 31 placing from 85 rides.

Her last competitive ride was at Bong Bong on November 24, while she rode Kirkup galloper On The Catwalk in a trial at Canberra last Friday.

Parkes trainer Sarah McIlrick was a big supporter of Johnson, and used her on eight occasions for five wins.

"She was the best," she said.

"She just knew what she was doing and could read the horses. She knew where to be every single time and it wouldn't matter what kind of mood the horse was in on the day, she could get along with it and win races.

"She was just a top chick, it's just absolutely tragic what has happened. I'm really speechless."

The Canberra training fraternity has rallied around Kirkup's stable, with Matthew Dale and Doug Gorrel among others helping work their stricken friend's horses on Monday.

Kirkup's star mare Highly Geared has been nominated to run at Rosehill on Saturday, and Canberra's trainers are determined to make sure she still races.

Highly Geared's owners are planning to meet at Rosehill on Saturday in memory of Johnson.

Stewards will decide later this week whether or not Highly Geared needs to race under the name of a different trainer.

Dale said the tight-knit Thoroughbred Park community had been left devastated by the events of Sunday afternoon.

"You see one another every day effectively, I've known Samara for many years and she's done a fair bit of riding for me, trackwork and jump-outs," Dale said.

"[She was a] beautiful girl that would always help out if we were ever stuck to get one worked or to jump one out, or have one at the barrier trials. She was always more than willing, it's just a complete tragedy.

"It's all pretty raw. Everyone just bands together here and does everything they can."

Senior trainer Barbara Joseph posted a heartfelt Facebook tribute saying Johnson was, "A shining light around Thoroughbred Park, a friend to all and one of the best trackwork riders and picnic jockeys we've seen".