As Michaela Banerji learned she would be at the centre of a High Court case testing freedom of speech, the former Immigration Department official entered another uncertain chapter since her sacking in 2013.

On a Sunday evening she meets at her home in Canberra's suburbs and is weighing up what could happen after Attorney-General Christian Porter intervened in her stoush with the federal government over her dismissal for the social media posts.

More than a week on from Mr Porter's decision in July to send the case to the nation's highest court interpreting constitutional matters, Ms Banerji is glad it will avoid the routine of appeals and legal argument that would have made its route there tortuous.

She also thinks it's a "two-edged sword". There's a cloud over what the High Court's judges might make of the government appeal against an Administrative Appeals Tribunal decision in April that set social media alight by finding the Immigration Department had unlawfully sacked Ms Banerji and intruded on her right to free political expression.

The tribunal's Deputy President Gary Humphries, and member Bernard Hughson, found almost all the reasons behind the restrictions in a code of conduct limiting freedom of speech for government officials did not apply to anonymous expressions of opinion.

"The burden of the code on Ms Banerji’s freedom was indeed heavy – the exercise of the freedom cost her her employment," they said.

"In our opinion, there is no significant justification available to the employer here for the law which exacted that cost."

Ms Banerji was caught off-guard by the appeals tribunal's blasting of the Immigration Department decision to dismiss her, which deputy president Humphries and Dr Hughson described as an Orwellian move resembling "thoughtcrime" in the dystopian novel 1984.

Previous court battles had lowered her hopes of success at the appeals tribunal. Federal Circuit Court judge Warwick Neville in 2013 rejected Ms Banerji's application for a stay on her dismissal, in a decision thought likely to curtail bureaucrats' use of social media.

Judge Neville found Australians had no ''unfettered implied right (or freedom) of political expression'', and she was later sacked for using Twitter to post anonymous but critical tweets about Australia's immigration detention policies.

Her tweets, sent between about January and July 2012, also criticised the government, the then-minister, and Ms Banerji's senior manager.

The dismissal still hurts Ms Banerji, who was unable to work in the Australian Public Service afterwards. She said colleagues abandoned her, and that she had to sell her unit as mortgage payments grew unmanageable. Depression and anxiety followed her sacking, the tribunal found.

"It drives a stake through you. It means everything you've believed in and worked hard for is just trashed," Ms Banerji said of her dismissal.

"It makes you feel ashamed and the internal conflict is ghastly because on the one hand you believe or want to believe or do believe that you've done nothing wrong and yet all these things externally are coming at you telling you that you've done something terribly wrong and you're being punished for it."

Ms Banerji approached her lawyer, Canberra-based Allan Anforth, believing her dismissal was unlawful by trespassing on her freedom of speech. Today she says the AAT decision agreeing with that - and finding the government's workplace insurer Comcare owed her compensation - initially made her feel worse.

"Psychologically, the AAT decision had an unsusual effect," she said.

"Right up until that point, there was always doubt in my mind that I could've been wrong, that I had done something wrong.

"But when the AAT said that I hadn't, that kind of made me feel worse for a while. For a while I kind of got over it but the immediate thing was, 'oh, I've been right all along, they were wrong all along' and the harm was real all along."

Comcare lost the appeals tribunal case, despite arguing it didn't owe compensation because the Immigration Department took reasonable administrative action by dismissing Ms Banerji.

The federal government is appealing the tribunal's decision, saying the Australian Public Service laws the department dismissed her under were reasonably designed to uphold public confidence in the bureacuracy and keep it impartial, apolitical and professional in serving ministers.

The Attorney-General's Department did not comment for this article although has previously said the case would influence how the government administered the Public Service Act across the public sector. The Immigration Department (renamed Home Affairs in December) said it did not comment on individual employment matters or cases before the courts.

Court documents show the government is arguing the appeals tribunal was right to find public service laws restricting officials from making political statements were reasonably appropriate for "open" comments, but that it erred in finding a distinction between these and "anonymous" comments not found in the statute.

The tribunal wrongly construed the legislation as laws trying to prevent anonymous expressions of opinion, regardless of the circumstances the opinion was expressed, the government says. Its lawyers will also argue the tribunal failed to consider whether there was any alternative measure that would have also upheld the public service's impartiality and professionalism.

Ms Banerji was working in the then-Department of Immigration and Citizenship, under the Gillard government, when she directed criticisms at Australia's asylum seeker policy under her pseudonym @LaLegale.

"Where states fail to offer legal asylum to refugees, that state fails," she said, among other tweets. She exhorted then-opposition Immigration spokesman Scott Morrison and then-Labor government Justice and Home Affairs Minister Jason Clare to read the international convention on refugees.

"DIAC doesn’t see the steps: 1. Is Oz first place of asylum? 2. Is person security cleared? 3. Is person risk persecution? #getitright," she posted.

In its findings, the appeals tribunal said Ms Banerji appeared to have taken care not to have used information which could only have been in her possession as an Immigration employee.

She said her tweets were meant to explain Australia's role as a signatory to the Refugee Convention, and to point out it was shirking the responsibilities this created.

"It was always about the law, it was always about the legal provisions," she said.

Ms Banerji said the points she made were even more important for Australia than for asylum seekers.

"It's Australia's integrity that's at stake here, Australia's legal and moral integrity."

Asked if her tweets undermined the department's ability to serve ministers in an impartial, apolitical way, Ms Banerji said the cynic in her believed the Gillard government had done enough to trash its own reputation and that the department had afforded her tweets more power than they really held.

"That's the kind of question that really doesn't have an answer, because you could take it from so many points of view," she said.

Ms Banerji said she had been committed to her department and always respected public servants.

Her lawyers want the federal government to pay her court costs regardless of the outcome, which they said would let them find a senior counsel experienced in High Court cases and equipped to argue her cause against the government's legal team.

The five-year battle with the government has at times left her exhausted but Ms Banerji says she would wake up after feeling dejected the night before and regather the motivation to fight on.

"I suppose if there's ever a story to be told, it's about the effect of litigation on a person which can actually be worse than the original insult, and have broader consequences," she said.

"People have said to me I'm brave. It's not really brave because at lots of points in the process you feel as though you can't go on or you don't want to go on," she said.

Later she says, "You get caught up and you keep on going", a comment that needs unpacking. Ms Banerji is aware what the High Court's decision on her case could mean for the federal government's 152,000 employees, and her lawyer Mr Anforth says it could also affect free speech for private sector and state government workers.

Since her dismissal the Coalition last year released a new social media policy limiting what public servants can say on forums like Facebook and Twitter, a move described as draconian by Labor and unreasonable by the Community and Public Sector Union.

Ms Banerji said she wished public servants would get on board with her cause.

"But the political atmosphere is not one that encourages that kind of participation.

"It's a Damoclean sword hanging over public servants' head, and if they have children they have to pay school fees for, they're not going to take a risk to make public commentary about government if it means that they're going to get the sack next week."

The Australian Human Rights Commission is also aware of the case's potential meaning, and intends to enter it making submissions about human rights issues it raises, including the right to freedom of expression and the right to participate in public affairs, while not representing Ms Banerji.

Coming back to her cryptic comment, she says she's motivated in her long fight by the influence it could have on free speech for public servants once the High Court reaches a decision.

"You start to see it as having repercussions outside your own experience and your own existence, and you can see that if you keep on going, that you might make a change that will affect others in a really good way."