Melbourne - The Australian owner of weekend family lunch is being tried at trial accused of murdering her estranged husband’s parents and an aunt and trying to murder the uncle with a poisonous mushroom.

Prosecutor Nanette Rogers filed a lawsuit against 50-year-old Erin Patterson in the Victoria Supreme Court on Wednesday. Patterson pleaded not guilty to all charges.

Rogers said she served beef Wellington meals, mashed potatoes and mung beans at her home in the rural town of Longarsha on July 29, 2023. Her guests include her parents Gail and Don Patterson, including 70-year-old Gail Patterson's sister Heather Wilkinson, 66-year-old Wilkinson's husband Ian Wilkinson, 68-year-old.

The next day, all four guests were hospitalized for poisoning of death cap mushrooms (also known as Amanita phalloides) and were added to beef and pastry dishes. Ian Wilkinson survived a liver transplant.

Erin Patterson's husband, Simon Patterson, 50, was also invited to lunch, but refused.

The jury was told Tuesday that prosecutors have dropped three charges of Erin Patterson trying to murder her husband, with whom she has been separated since 2015.

Two weeks before the poisoning, Erin Patterson invited her husband and his relatives to lunch, while she attended Korumburra Baptist Church service where Ian Wilkinson served as pastor. Simon Patterson initially accepted the invitation.

"She said the purpose of lunch was to discuss some of the medical issues she had and to break it down to the kids," Rogers said.

Rogers added: "The defendant said it is important that the children are not at lunch."

The Wilkinsons were surprised by the invitation because they had never been to Erin Patterson’s five-bedroom building.

When Heather Wilkinson was taken to the hospital the next morning, she told Simon Patterson that she was confused about Erin Patterson's diet, which served guests with the plates.

Prosecutor Heather Wilkinson said: "I noticed Erin put the food on our plate. Her plate had color. I wonder why that was. I've been confused about it since lunch."

Simon Patterson told his aunt that his wife might have run out of plates.

Rogers told the jury that Erin Patterson created a diagnosis of ovarian cancer to explain why her child was not attending lunch.

"After lunch, the defendant announced she had cancer and asked for a question about whether to tell the children or stay in touch with them," Rogers said.

Rogers added: "They'd better be honest with the children. They pray for the health and wisdom of the defendant."

Two days after lunch Erin Patterson went to the hospital to complain about diarrhea and nausea. By then, medical staff had diagnosed her guest with death cap poisoning.

Erin Patterson told authorities she cooked it with fresh mushrooms purchased from a supermarket and dried mushrooms purchased from Asian food stores. She cannot identify the Asian business.

Doctors insisted that Erin Patterson's two children, 9 and 14, were employed by their mother because they said they had leftovers of beef.

Erin Patterson said the kids were safe because she scraped pastries and mushrooms from the steak. She explained that the kids don’t like mushrooms.

"The defendant became tearful and said she didn't want the kids to participate," Rogers said.

"She doesn't seem to care so much about the health of her children, but rather emphasizes them," Rogers added.

Erin Patterson hasn't eaten poisonous mushrooms or given the kids leftovers for lunch, Rogers said.

Prosecutors said health authorities regarded the poisoning as an isolated incident and did not recall mushrooms.

The trial is expected to last for six weeks. She was charged with three counts of murder and one count of attempted murder. The maximum penalty for murder is the case, life imprisonment and attempted murder will be imprisoned for up to 25 years.