Patterson, who was sentenced to life behind bars after serving her lunch guests a death cap mushroom-laced meal, 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 be reading over notes as the courtroom filled with the members of the public and journalists who had been queuing outside for close to an hour.
Her surviving victim Ian Wilkinson and other members of the Wilkinson and Patterson families were also seated in the front row as lawyers began their arguments.
Patterson's new barrister Richard Edney started by attacking the integrity of his client's trial because of the jury sequestration.
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.
Mr Edney told the court that decision was "catastrophic" as it could have resulted in inappropriate communication or subconscious influence.
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.
Patterson's legal team will argue further appeal grounds over the next two days, including that she suffered a substantial miscarriage of justice due to an "unfair and oppressive" cross-examination.
Victoria's top prosecutor will then launch into the Crown's own appeal against Patterson's sentence.
Brendan Kissane KC is expected to argue 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 the July 2023 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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