Australia's worst female serial killer has, for the first time, woken to the possibility her convictions could be overturned — and according to one of her barristers she is "absolutely delighted".

Behind the forbidding outer fences at Cessnock Correctional Centre, Kathleen Folbigg is serving a 30-year prison sentence for the murder of three of her infant children and the manslaughter of a fourth.

The ABC this morning spoke one of Ms Folbigg's barristers, Isabel Reed, who said she spoke to Ms Folbigg about yesterday's news.

She said they both "shared the joy".

"It was a wonderful moment," Ms Reed said "I was absolutely delighted [about the news], as was Kathleen herself," she said.

Ms Reed, one of three barristers in Ms Folbigg's corner, said they believed there was enough evidence that is was "worth another look".

"Given that the medical and scientific research has moved on considerably since her trial, we now believe that we have compelling evidence that none of her babies were smothered," she said.

"In the end it's a matter of justice. [And] we believe we have all our ducks in a row."

A tragedy beyond imagination

For many, when her case came to trial in 2003, she became a figure of hate.

Yesterday's decision by NSW Attorney-General Mark Speakman to order a judicial inquiry into her convictions marks the latest chapter in a long campaign by her legal team to have her case — and the evidence that convicted her — re-examined.

"Whatever view you take of this case it is a tragedy beyond imagination," Mr Speakman said.

He added: "It is an incredibly important decision, with significant consequences for Ms Folbigg who is incarcerated, and for her family who have been through unimaginable tragedy."

Former District Court chief judge Reginal Blanch will conduct the inquiry.

It is expected to take between six months to a year to complete, during which Folbigg will continue to serve her sentence.

Sorry, this video has expired Kathleen Folbigg speaks about her guilty verdict

Mr Speakman said the decision weighed heavily on him.

"But ultimately my job as Attorney-General is to ensure public confidence in the administration of justice in New South Wales."

The announcement comes three years and three months after a petition was lodged on Folbigg's behalf with the Governor of NSW by her legal team.

On Australian Story last week, former NSW DPP Nicholas Cowdery said in his view this had been an "inordinate" delay.

Mr Speakman said Mr Blanch will be asked to focus in particular on one specific area of evidence presented to the jury at trial by the state's chief prosecutor, Mark Tedeschi.

"The petition appears to raise a doubt or question concerning evidence as to the incidence of reported deaths of three or more infants in the same family attributed to unidentified natural causes in the proceedings leading to Ms Folbigg's convictions," Mr Speakman explained.

Ms Folbigg's petition goes further: "The proposition that there had never been more than three SIDS deaths in a family was allowed into evidence. This was damaging evidence that raised and reinforced tendency and coincidence reasoning, and was wrong."

(Clockwise from top left) Patrick, Laura, Caleb and Sarah Folbigg, who a court found were killed by their mother. ( ABC News )

Author and law academic Emma Cunliffe highlighted the discrepancy to Australian Story.

"I think that the most striking evidence that the jury heard was from medical witnesses, each of whom was asked by the prosecution whether the medical literature documented three or more sudden, unexplained deaths in a family, being natural deaths," she said.

"Every medical witness answered 'no' to that question.

"I think that the jury would have found that that really compelled a conclusion that the children were killed. In fact the medical literature documented cases of natural unexplained deaths in families, three or more such deaths, and since the time of the trial, more cases have been documented."

The inference from some medical experts at the trial was that, although there had been published reports of three or more unexplained child deaths in individual families, they had not — in their view — been substantiated as having met the accepted, formal definition of sudden infant death syndrome (SIDS).

These claims were never fully explored.

As Ms Folbigg's petition puts it: "Throughout this case, the prosecution placed emphasis on the claim that three or more unexpected deaths from natural causes in a family had never occurred."

Prosecution analogies criticised

The petition claims Mr Tedeschi effectively "reversed the onus of proof and engaged in misleading analogies to support his central point".

The most dramatic of these analogies was when Mr Tedeschi suggested, in his closing address to the jury, it was possible that all four of Kathleen Folbigg's children had died from natural causes.

"I can't disprove any of that, but one day some piglets might be born from a sow, and the piglets might come out of the sow with wings on their back, and the next morning Farmer Joe might look out a kitchen window and see these piglets flying out of his farm," he said.

"I can't disprove that either."

Mr Cowdery is critical of Mr Tedeschi's use of the analogy.

"I don't think it would have been unnecessarily prejudicial," he said.

"It was unnecessary. It was unfortunate."

Mr Tedeschi declined to be interviewed on Australian Story.

Legal team, supporters welcome inquiry

Folbigg's legal team has been cautiously optimistic after the Attorney-General's announcement.

"We are obviously pleased that the Attorney-General has decided to have an inquiry," barrister Robert Cavanagh told the ABC.

"Kathleen Folbigg's solicitor will be making representations about procedural matters and the scope of the inquiry."

In a phone call recorded by the ABC, Folbigg described what it was like when she was sitting in the dock during her trial in 2003.

"I think I just kept thinking to myself: 'No, no, no, I have full faith in this justice system'," she said.

Mr Speakman said that at the conclusion of the inquiry, Mr Blanch would make a recommendation to the Governor.

"If he considers that there is reasonable doubt about Ms Folbigg's convictions, then that matter may well be referred to the Court of Criminal Appeal."

Folbigg says she has been "clinging to that little bit of hope".

"If I can get myself heard in any way, then I guess my last 15 years in prison will have been worth it," she said.