Erin Patterson has lost her bid to overturn her convictions and been resentenced to life behind bars with no chance of release, as Victoria’s highest court handed down its decision on two appeals regarding her triple murder case.

The court of appeal ruled on the two appeals on Friday, after justices Lesley Taylor, Stephen McLeish and Peter Kidd heard arguments from her legal team and prosecutors in August.

Patterson, 52, did not attend the 15-minute court hearing in person, and showed no emotion on the video feed as McLeish outlined why her appeal had failed, and how the director of public prosecutions had succeeded in seeking a longer sentence.

Patterson was last year sentenced to life imprisonment, with a non-parole period of 33 years, for the murders of her estranged husband’s parents, Don and Gail Patterson, and his aunt Heather Wilkinson, after she hosted them for lunch.

She was also convicted of the attempted murder of Heather’s husband, Ian Wilkinson, who survived the beef wellington laced with death cap mushrooms after spending weeks in hospital.

McLeish said the court had granted leave to appeal on the first two grounds of Patterson’s appeal, but dismissed the appeal, and dismissed the five other grounds raised by her lawyers.

He said the court granted the DPP appeal against the sentence, however, as it was clear the original sentence did not properly reflect the seriousness of her offending.

McLeish said Patterson sustained an intent to murder all four people for three weeks, from the time they were invited to the lunch, during the meal, and during the “protracted suffering and ultimate deaths that resulted”.

The offending was “carefully planned and deliberate”, he said, and involved an “elaborate series of deceptions” including claims that she had cancer, denying she had foraged mushrooms, and lying about the source of the mushrooms.

“This offending was extraordinarily cold and calculated, and stands to be denounced in the strongest possible terms,” McLeish said.

When the judges left court, Patterson also stood, took a book from beside her, and walked off-screen.

In the courtroom, family members hugged and were emotional, and detectives involved in the case looked elated. Nobody commented outside court.

Patterson now must apply to the high court for leave to appeal, should she wish to continue fighting her conviction or new sentence.

She is one of only a handful of Victorian offenders sentenced to life without parole, and one of the only women in Australian history to be given the sentence.

Written reasons for the decision were provided to media later on Friday.

In them, the court said while the first ground of the DPP’s appeal – that trial judge erred in finding that there was a substantial chance Patterson would be in solitary confinement for much of her sentence – had failed, it was clear the second ground, that the sentence was manifestly inadequate, should succeed.

The court found they were “heinous crimes” and “we are driven to conclude that a non-parole period of 33 years fails to reflect the calculated criminality of the applicant in committing three murders and attempting a fourth”.

“The offending was carefully planned and deliberate. It represented a cruel breach of trust to members of the applicant’s extended family,” the court found.

“The taking of three lives (and the attempt on another) in these circumstances called in our view for much stronger denunciation.”

In relation to Patterson’s appeal, the court described many of the grounds as having no substance, being without merit, or even fanciful.

In relation to the ground that the sequestering of the jury in the same hotel as the police informant and members of the prosecution amounted to a substantial miscarriage of justice, the court found that it “was plainly unfortunate that [the] situation arose”. It said it was “highly undesirable” and “the judge would not have countenanced this arrangement if approval for it had been sought in advance”.

But the justices said there was no evidence any wrongdoing had occurred.

“The accommodation arrangements offered fertile grounds for speculation but no objective basis for the fair-minded person to reasonably apprehend that the jury might not have discharged its function of rendering a verdict according to law. “

In relation to ground two – that undue weight was placed on evidence given by a telecommunications expert that raised the possibility she visited two sites where death cap mushrooms had been reported – the court found the probative value of the evidence was not outweighed by the danger of unfair prejudice to Patterson.

In August, the court heard Patterson should have been given no possibility of ever being released from prison, or a non-parole period so lengthy that she was likely to die behind bars.

Her lawyers argued seven grounds for her appeal, including that allowing jurors to stay in the same hotel as police and the prosecution while they deliberated over their verdicts in the triple murder trial represented a “catastrophic” failure of the justice system.

Richard Edney, for Patterson, had said the failure to properly separate the jury during their deliberations was a fundamental irregularity that had denied her a fair trial.

“What we say has occurred here in the applicant’s trial was an inexplicable and perhaps still unexplained failure of a process,” Edney told the court in August.

During the hearings, Brendan Kissane KC, the DPP, said that even though Patterson would be aged in her 80s by the time she was eligible for parole, her sentence was still too lenient.