A Western Sydney woman who allegedly decapitated her mother explosively lashed out in “rage attacks” as part of complex mental disorders, a court has heard.

WARNING: This story contains graphic content that some readers may find upsetting.

Forensic psychiatrist David Greenberg described Jessica Camilleri as “a very complex mental picture”, with multiple primary diagnoses complicated by associated features, such as narcissism.

The 27-year-old has pleaded not guilty to murdering her mother, 57-year-old Rita Camilleri, by repeatedly stabbing her and cutting off her head with knives in a St Clair home last July.

Mental illness is at the centre of Ms Camilleri’s defence and the jury was asked to consider whether the charge should be reduced to manslaughter.

“There’s no one disorder that describes her,” Professor Greenberg told the NSW Supreme Court on Friday.

After two examinations, he considered her primary diagnoses were intellectual disability disorder, autistic spectrum disorder, and intermittent explosive disorder.

Ms Camilleri was bullied for nearly her entire school life and learned to deal with her problems through targeted aggression, he said.

“When she reportedly lashes out, she loses control as part of her intermittent explosive disorder,” Professor Greenberg told the jury.

“She is prone to explosive outbursts where there is a failure to control impulsive aggressive behaviour.”

Rita Camilleri’s body was found in the kitchen of her home at St Clair.

Such outbursts were “anger-based rather than pre-meditated and instrumental”, he added.

Professor Greenberg said Ms Camilleri could be provoked by something as simple as a stranger looking at her the wrong way.

But he said if anyone touched her or did anything physical, she would “lose all control”.

“You could say it’s like a rage attack, but in the explosive extreme form.”

Ms Camilleri had an “unreasonable expectation of favourable treatment”, “a history of demanding attention” and “poor self-esteem [but] a sense of entitlement”, the jury heard.

The defendant’s disorders caused repetitive, fixated interests, according to the professor.

The court previously heard Ms Camilleri had a fascination with horror movies and would repeatedly watch The Texas Chainsaw Massacre.

During one of her interviews with Professor Greenberg, she admitted her macabre act of beheading her mother was inspired by such films.

She would also spend hours a day prank calling strangers and making threats of extreme violence against them, which Professor Greenberg believed was another fixated interest.

Two tests have previously measured Ms Camilleri’s IQ as 64 and then 55, which Professor Greenberg said placed her “in the lowest one per cent of the population in terms of her cognitive capacity”.

The court has heard she stopped taking psychiatric medication six months before the incident in favour of seeking natural alternatives.

The trial, before Justice Helen Wilson, continues.

Family and domestic violence support services:

• 1800 Respect national helpline: 1800 737 732
• Women’s Crisis Line: 1800 811 811
• Men’s Referral Service: 1300 766 491
• Lifeline (24 hour crisis line): 131 114
• Relationships Australia: 1300 364 277

-ABC