An Australian woman accused of murder has denied she deliberately included poisonous mushrooms in a lunch she served to three elderly guests, as the prosecution wrapped up five days of cross-examination.

Erin Patterson is charged with the murders of her mother-in-law Gail Patterson, father-in-law Donald Patterson and Gail's sister, Heather Wilkinson, along with the attempted murder of Ian Wilkinson, Heather's husband, in July 2023.

Crown prosecutor Nanette Rogers SC rounded out her marathon cross-examination on Thursday with three suggestions – that Patterson deliberately sourced death cap mushrooms in 2023, deliberately included them in the beef Wellington she served her former in-laws and did so intending to kill them.

The prosecution accuses her of foraging for the death caps, before drying them and knowingly serving them in individual portions of Beef Wellington at her home in Leongatha, a town of about 6000 people some 135km (84 miles) from Melbourne.

Patterson denies the charges, which carry a life sentence, with her defence calling the deaths a "terrible accident".

Rogers ended her cross-examination by accusing Patterson of deliberately sourcing the mushrooms for the lunch.

"I suggest you deliberately included them in the Beef Wellington you served (the guests) ... you did so intending to kill them."

"Disagree," the accused replied.

The 50-year-old was asked about her evidence that she dehydrated dried mushrooms she had bought from an Asian grocer before adding them to the beef Wellingtons.

She agreed she never said this to anyone at the time and didn't mention putting the fungi into the dehydrator when she earlier admitted adding them to the lunch.

"I suggest this is another lie you made up on the spot," Rogers said, accusing Patterson of hedging her bets to try to make it sound like there were multiple possible sources for the death cap mushrooms.

"Incorrect," Patterson responded.

Ian Wilkinson, who survived ingesting the mushrooms, outside court. – AAP

She also denied that she "deliberately concealed" one of her phones, referred to at the trial as phone A, from police when they searched her house. 

Patterson said she switched from phone A to another, referred to as phone B, because the former was "not cutting it anymore".

But the prosecution pointed to records that showed regular use from a SIM card in phone A until days after the mushroom lunch.

Patterson said she conducted a factory reset of phone B because she wanted to use it and that was the phone she gave police.

"I suggest to you that there was nothing wrong with phone A and this is another lie," Dr Rogers said.

"Disagree," Patterson responded.

The lengthy cross-examination followed three days of questioning from the 50-year-old's own barrister, Colin Mandy.

Erin Patterson was the only witness called by her defence, and her decision to take the stand reignited interest in the trial, now in its seventh week.

Media have descended on the town of Morwell where the trial is being held, about two hours east of Melbourne.

The jury is next expected to hear closing arguments from the prosecution and defence, before presiding judge Justice Christopher Beale gives his instructions to the jury.

The trial is expected to conclude later this month.