The so-called Christchurch 'Black Widow' has won the right to test body samples from her husband who she was found guilty of fatally poisoning.
Helen Milner was convicted of Phil Nisbet's murder in the Christchurch High Court in 2013, and was sentenced to a minimum of 17 years. She failed in an appeal against her conviction.
She was found guilty in 2013 of administering a fatal dose of anti-allergy medication phenergan.
Her new defence is that Nisbet may not have ingested a fatal dose of phenergan and died from a latent heart condition.
She was sentenced to 17 years in prison but continues to maintain her innocence. She appealed her murder conviction from behind bars unsuccessfully - but now she's trying another avenue.
Counsel for the Nisbet family Nikki Pender told Newshub that Milner's latest defence theory is "mischievious".
Nisbet's sister Lee-Anne Cartier said in October the situation was "insane".
Cartier fought for police to investigate her brother's death, which was originally ruled a suicide.
"It's insane to think that this long it's still going on," she told Newshub.
"To say that he died of a heart attack and to say that there is evidence of anything pre-existing is just a total waste of taxpayers' money."
At the time of Milner's sentencing in 2014, Justice David Gendall described her offending as a "despicable crime" and a tragedy.
"This was a carefully planned and carefully executed murder," he told the court. "Death by poisoning has always been seen as the most despicable of crimes.
"Mr Nisbet was particularly innocent with no clear indication other than a monetary incentive as to why he was killed."