The caravan Charlise Mutten's mother was believed to be staying in at the time of her daughter's death has been declared a crime scene and is now under police guard.
Detectives and forensic officers spent hours swarming every inch of the white 1970s caravan and a nearby cabin at the Riviera Ski Garden, on the banks of the Hawkesbury River, on Friday.
Officers took away multiple bags of potential evidence for forensic analysis.
The Daily Telegraph earlier revealed police believe Kallista Mutten had been staying there on the night her daughter was allegedly killed by Justin Stein more than 80km away in the Blue Mountains.
Charlise is believed to have spent some time at the caravan park with her mother in the days before her death, and the park's owner confirmed to The Daily Telegraph he had spoken with police in relation to their investigation.
Homicide detectives are still waiting to speak to Charlise's mother, who remains in hospital.
It's believed Mutten suffered a medical episode during informal police questioning, which resulted in her being taken to Blue Mountains Hospital at Katoomba.
Police allege Charlise was murdered in the NSW Blue Mountains by her stepfather Justin Stein, who has been charged over the child's death.
In the lead-up to her death, police believe Charlise was spending time between the Riviera Ski Gardens and a sprawling estate at Mount Wilson, both owned by the family of Stein, Nine News reports.
The investigation continues as police try to figure out why the nine-year-old was left in the care of Stein in the Blue Mountains last Tuesday night while her mother stayed in the run-down caravan on the river.
On Wednesday, Deputy Commissioner Dave Hudson said it had been "difficult" to speak with Charlise's mum in the lead-up to Stein's murder charge.
"It has been difficult to approach and contact her but at some stage hopefully when doctors allow, we will be talking further with her," he said.
Police have no evidence to suggest that Mutten was involved in her daughter's death.
Detectives will allege in court that Stein had driven to Sydney with Charlise's body in the back of his boat, with police believing he had tried to launch it from an inner-Sydney dock, an exclusive report by The Daily Telegraph revealed earlier this week.
Authorities found her body inside a barrel on Tuesday near the Colo River, 76km from Sydney.
While the schoolgirl normally lived with her grandmother in Coolangatta, Queensland, she was spending two weeks with her mother during the school holidays.
University of Newcastle criminologist Dr Xanthe Mallett said it is "quite unusual" for there to be such a long period of time between the child disappearing and it being reported to police. She also said the first 24 hours after a child disappeared were often critical to the investigation.
"I think what is unusual is that she wasn't reported missing for a number of hours. That is quite unusual in a child disappearance," she told Sky News.
"However, we don't know why that was."