Registered nurse Cindy Munro told the Supreme Court she treated Patterson when she was admitted to Leongatha Hospital in Victoria's southeast on July 31, 2023.

Her former in-laws, Don and Gail Patterson, and Gail's sister, Heather and her husband, Ian Wilkinson, were already in the hospital after eating the poisoned beef Wellington at Erin's home on July 29.

Don, Gail and Heather all died in the days after the lunch, while Ian survived.

Patterson was charged with three counts of murder and one count of attempted murder but has pleaded not guilty to all charges and is on trial in Morwell.

Ms Munro told the jury she assessed Patterson about noon on July 31 after being involved in the treatment of Ian and Heather earlier that morning.

Patterson reported having nausea and diarrhoea, but the nurse said her appearance was different from the other lunch guests.

"She didn't look unwell like Heather and Ian," Ms Munro told the court.

"I recall Ian being so unwell he could barely lift his head off the pillow ... but Erin was sitting up in the bed, in the trolley, and she didn't look unwell to me."

The nurse said Patterson tried to refuse IV fluids and a recommended liver medication, but ultimately complied after medical staff insisted.

Patterson also advised Ms Munro that her children had eaten the lunch leftovers the next day.

The trial continues.

With AAP.