Evans, who has pleaded guilty to the strangling murder of Colleen Ayers, is set to testify in the NSW Supreme Court against a co-accused, Micheal John Duffy, on Wednesday.

The Crown alleges Evans and Mr Duffy together killed 33-year-old Ms Ayers and buried her in a shallow grave on her parents' Lakesland property, south of Sydney, in May 2012.

Another man, Scott Derbridge, has pleaded guilty to a charge of accessory to murder.

A young woman, who cannot be identified for legal reasons, took drugs and drank large amounts of alcohol with the group in the lead up to the murder.

In evidence, the young woman recalled that the day before the killing, Evans was reading a book at a train station called "Australia's Worst Serial Killers, or murderers, or something".

"She refused to let me look at it," the young woman said.

"Then she started going on about how Ivan Milat was in that book and told me 'I used to try and write to him but they would send the letters back'."

The young woman told the court she had frequently heard Evans say: "I always wanted to be a serial killer." The young woman said she never took Evans seriously.

The jury has been told Ms Ayers invited Evans, Mr Duffy, Derbridge and the young woman back to the property on May 9, after a day of using drugs and having a threesome.

Ms Ayers met the group at a pub in Picton.

The jury heard evidence that the group caught a train to Campbelltown and checked in to a hotel for the night. They used drugs including methylamphetamines (ice).

The young woman told the jury she was forced to film Mr Duffy, Ms Ayers and Evans having sex.

She said Ms Ayers was tied up using bed sheets and Mr Duffy and Evans performed various sex acts on her.

"Things kinda got out of hand … I was 16, I'd never see anything like that in my life," she said.

"I was just off my head like everyone else."

The next morning the group bought drugs to share in a Campbelltown park. Ms Ayers suggested they go to her parents' property as they were travelling interstate.

Last week, Ms Ayers' stepmother, Judith Green, gave evidence that the 33-year-old was not allowed at the property alone and had been prohibited from inviting guests over. Ms Ayers had long-standing mental health and substance abuse issues and had recently been in drug rehabilitation.

The young woman told the court that that evening the group, including two other men, caught a taxi to the Greens' property, where they lit a bonfire, and started drinking in the guest house.

The young woman said Ms Ayers "looked hammered". Evans told the young woman she had given Ms Ayers 100 mls of methylated spirits via a needle, telling Ms Ayers it was ice.

In her evidence, the young woman said that later, Mr Duffy and Ms Ayers could be heard having sex in a bedroom of the guest house and Evans became agitated.

"Rachael lost the plot," the woman said.

"She was saying, 'I'm going to do it, I'm going to do it'."

Evans got a leather belt and went into the bedroom.

"All I heard was Debbie yelling, 'please no'," the woman said.

She went into the bedroom and turned on the light. Evans said to her: "Don't look at the body."

The woman said Ms Ayers' body was slumped on the bed.

Mr Duffy has pleaded not guilty to murder.

The trial continues before Justice David Davies.