Mrs Green, her husband and Ms Ayers' father Bryon​ Green, and the young relative were enjoying an interstate holiday in May 2012 when their caretaker rang to tell them their 25-acre property at Lakesland, south of Sydney, had been ransacked.

The trio continued their holiday and on their return in late May 2012, they discovered two firearms were missing as well as jewellery. The study of the main house had been turned upside down and a pair of Ms Ayers' jeans were found in a bathroom of the guesthouse on the property, the NSW Supreme Court was told.

As days went by and Ms Ayers still failed to get in contact, Mrs Green's fears grew.

Ms Ayers, who had a history of mental illness and who had spent part of 2012 in drug rehabilitation, had been prohibited from being in the house alone and banned from inviting anyone over while her parents were away.

Unbeknown to her parents, on May 9, Ms Ayers had invited a group of people back to the property after a day of using drugs and having a threesome.

She was then allegedly murdered during a sexual encounter with Micheal​ John Duffy and buried in a shallow grave near a dam.

Mr Duffy, 34, has pleaded not guilty to murder. He is accused of helping another woman, Rachael Margaret Evans, strangle Ms Ayers before they robbed the Greens' house late that night.

The jury has been told that Evans has pleaded guilty to Ms Ayers' murder and will give evidence that she burst in on Mr Duffy and Ms Ayers as they had sex and started choking her with a leather belt.

Giving evidence on Thursday, Mrs Green said police asked the family to vacate the property on May 31. She and her husband checked into a motel.

At 2am on June 1, homicide detectives knocked on the door. "They told us they had found a grave," Mrs Green said.

The trial before Justice David Davies continues.