Helen Cummings celebrates her friend Kathleen Folbigg's release from prison

The campaign began after a 2011 book by an Australian academic lawyer, Murder, Medicine and Motherhood, concluded Folbigg was wrongly convicted.

Ms Cummings began the crusade with a letter to then NSW Attorney General Greg Smith in 2013, after a year of corresponding with and visiting Ms Folbigg.

Helen Cummings is thrilled at the news of her friend Kathleen Folbigg's unconditional pardon, and release from prison, after 20 years.

"We were sorting out a new petition, and now we don't have to," Ms Cummings said from her Newcastle home.

"She's only just been released now, she is being picked up by her best friend.

"I am still coming to terms with it. It's been too long, 20 years for something she didn't do but, I've been visiting her and corresponding with her and phoning her ... for the last ten years.

"There have been many disappointments along the way. The first inquest was a very big disappointment, when (then Chief Judge of the District Court, Reginald Blanch AM QC) said he wasn't interested in the content of her diaries, which just broke our hearts."

The second inquiry was a different kettle of fish, Ms Cummings said, when Sophie Callan SC, assisting the inquiry, said the conclusion had been reached that there was substantial evidence pointing to reasonable doubt about Ms Folbigg's guilt.

"So when she said those words, I thought this is the beginning, it's going to still take time, but for her to say that, and then the DPP, who had been fighting to keep her there, agreed, we knew, yes.

"Thanks to the scientists and the new evidence, all of this new evidence that proved beyond doubt that the two girls had died of natural causes and the two boys, there was a gene ... to show epilepsy was the cause of the death of one of the boys."

Ms Folbigg was charged over the deaths of all four children, so as soon as one of those had fallen over on the evidence, the other three should have fallen, but nonetheless the battle was over, Ms Cummings said.

"It's just the best news," she said. "I can't wipe the smile off my face. I had tears in my eyes when I found out but now I can't stop smiling.

"It's a big day here for Kathleen, justice at last has been served and it's taken too long but it's happened, and my thoughts are with my friend.

"I hope she is sitting up to a T-bone steak right now and a bath."

Ms Cummings, the daughter of former Newcastle lord mayor Joy Cummings, sent a copy of her book Blood Vows, to Folbigg in early 2012 ''to let her know where I was coming from''.

Blood Vows tells the story of her first husband's murder of his second wife and young daughter, and suicide,

Her first meeting in Silverwater jail started with ''a hug for a long time''. In letters and monthly meetings between them since, ''nothing has been off limits''.

But the groundwork of an appeal for a review of Ms Folbigg's case had already been done in Dr Emma Cunliffe's book, Ms Cummings told the Newcastle Herald in 2013.

''I contacted Emma because I always had an uncomfortable feeling during Kathleen's trial that it was actually her mothering that was on trial.

''She was totally hated and despised by society, and locked away.

''We saw that with Lindy Chamberlain, and the same thing ... happened to poor Kathleen.''

The matter would now need to proceed to the Criminal Court of Appeal for the conviction to be quashed, Ms Cummings said.

"The governor Margaret Beazley doesn't have that power, and the Attorney General doesn't have that power. That power sits with the Criminal Court of Appeal and I will be hoping beyond hope they will quash it."