Sharon Graham is serving a life sentence after being found guilty of murder following her grisly plan to kill her ex-partner Bruce Saunders for insurance money.
Graham has appealed against her conviction, years after Mr Saunders was fed into an industrial woodchipper on a Sunshine Coast property in Queensland.
In an attempt to make it look like an accident, all that was left of his body were the legs.
Graham's partner Greg Roser is also serving a life sentence for murder after he beat Mr Saunders with a metal bar and fed the body into the machine with the help of another man, Peter Koenig, in November 2017.
Koenig received a lesser sentence for being an accessory to murder after an undertaking he testify in Roser and Graham's trials.
Graham's barrister Andrew Hoare KC on Friday told the Queensland Court of Appeal his client had been the victim of a miscarriage of justice.
He argued there had been an error of law in that Justice Martin Burns had failed to direct the jury at Graham's 2023 trial in relation to a claim of privilege by Koenig which may have affected the verdict.
Koenig, a truck driver, had claimed privilege against self-incrimination when asked whether he knew there was cannabis on board his vehicle.
Mr Hoare said the jury could only have reached a guilty verdict if it was convinced of Koenig's credibility.
But he argued Koenig's claim of privilege put his credibility as a witness in question.
The bench, comprising Justices Debra Mullins, John Bond and Shane Doyle, responded by calling Koenig a "grub".
"If the inference was open from the circumstances that Mr Koenig might have been a drug trafficker of cannabis, how does that realistically affect the reasoning of the jury in this trial?" Justice Bond asked.
"This was a guy who, on his version of events, was an accessory after the fact to putting a person someone else had killed to cover up that person's crime - he was a grub!"
Justice Doyle said if Koenig was "a noted drug trafficker", it suggested he was more likely to have been involved in the plot to kill Mr Saunders.
"People don't approach stand-up citizens in the street to commit murders of their ex-boyfriend," he said.
The bench reserved its decision.
Roser's appeal against his life sentence was dismissed in February.
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