Patterson, who was sentenced to life behind bars after serving her lunch guests a death cap mushroom-laced meal in July 2023, is fighting to quash her convictions in the Victorian Court of Appeal.
She did not appear at court in person on Wednesday, instead watching the hearing on a video link from the Dame Phyllis Frost Centre.
Dressed in a royal blue jumper, the 51-year-old murderer appeared to read notes and at times closed her eyes as a courtroom full of members of the public and journalists watched on.
Her surviving victim Ian Wilkinson and other members of the Wilkinson and Patterson families were also in attendance, more than three years after the fatal lunch.
One of Patterson's new barristers Veronika Drago argued her client suffered a substantial miscarriage of justice in her trial because she was "forced" to give evidence.
Ms Drago pointed to rulings from the trial judge, who did not allow mushroom photos from 2020 found on Patterson's SD card into evidence.
The defence wanted to use those photos to show Patterson always had an interest in foraging for mushrooms, Ms Drago said.
Without the images, there was only one way jurors could hear evidence of foraging, the court was told.
"It compelled (Patterson) to give evidence on this issue," the barrister said.
"That fundamentally altered what she was forced to address while she was giving evidence."
Ms Drago submitted Patterson's right to silence was compromised as a result.
The integrity of the trial was also attacked due to how the jury was sequestered.
Jury members remained together during their deliberations but ended up staying in the same hotel as the lead investigator and members of the prosecution team.
That decision was "catastrophic" as it could have resulted in inappropriate communication or subconscious influence, defence barrister Richard Edney said.
When Justice Peter Kidd questioned whether there was any evidence of communication between jurors and the parties, Mr Edney said there was not.
But he maintained it was still a failure of process that had not been explained by the prosecution and should lead to a re-trial.
"It does amount to a fundamental irregularity," Mr Edney said.
Mr Edney also argued the cross-examination of his client had been unfair and oppressive, with the prosecutor repeatedly asking whether other witnesses were wrong, mistaken or correct.
The prosecution closing address was also "problematic," he said.
Patterson's lawyers will finish their appeal arguments on Wednesday afternoon before Victoria's top prosecutor responds.
Brendan Kissane KC will then appeal Patterson's sentence on the ground her 33-year non-parole period was manifestly inadequate.
A jury found Patterson deliberately served beef Wellingtons laced with death cap mushrooms to her former in-laws Don and Gail Patterson, 70, and Gail's sister Heather Wilkinson, 66.
The three guests died after lunch at Patterson's Leongatha home, in regional Victoria, while Heather's husband Ian fell seriously ill from the meal but survived.
Patterson was also convicted of Mr Wilkinson's attempted murder.
The appeal hearing before Justices Stephen McLeish, Lesley Taylor and Peter Kidd continues.
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