Several knives were allegedly used during the course of the incident, which Detective Superintendent Brett McFadden described as "one of the most significant, most horrific scenes police have had to face".
Superintendent McFadden said the woman was fatally injured after "an argument that became violent".
"There is no stepping away from the fact that this was horrific and a significant attack, and the injuries that the victim suffered were extensive," he said.
Jessica was arrested at the scene and charged with murder.
During her court appearance she pleaded for medical attention at Parramatta Local Court on Sunday afternoon, when she appeared via audiovisual link from the Amber Laurel Correctional facility at Emu Plains.
"I really need medical attention ... I cannot move my fingers because of the incident that happened," she said.
"I couldn't even wash myself properly when I had to shower to get all the blood off."
Ms Camilleri's lawyer told magistrate Michael Price his client suffered from "severe mental health issues", according to the SMH.com.au report.
Attending police and paramedics are receiving support following the incident.