A woman accused of sexually abusing male primary students while working at their NSW school had a "rich fantasy life" and liked to dress up as Marilyn Monroe, a Sydney court has heard.

The woman, known only as "CJ", was sentenced to a minimum of five years in prison in 2011 for sexually abusing a number of boys over five months in 2009 while working as a weekend "housemother" at a southern NSW school.

But her convictions were quashed last year after the Court of Criminal Appeal found the original judge failed to properly analyse evidence of her mental state at the time of the offences.

At the judge alone re-trial on Tuesday, forensic psychiatrist Professor David Greenberg rejected claims the 44-year-old woman suffered from bipolar disorder, saying she suffered "no defect of reason".

Prof Greenberg told Downing Centre District Court that CJ had been "contaminated" by her research into bipolar, such as doing quizzes on the Black Dog Institute website.

While CJ "identified" with symptoms of bipolar, Prof Greenberg said he believed she displayed "cognitive and personality disturbances" similar to those seen in female pedophiles.

"It wasn't just sex ... she believed that she was having a relationship with this child and that the child was her lover."

He said CJ further believed the then 11-year-old boy had been the one pursuing the affair.

Prof Greenberg added there were numerous examples which would suggest CJ knew of her wrongdoing, telling one of the boys that if anyone found out about them she would go to jail.

The former school employee reported having a "rich fantasy life" and had been known to dress up as former screen siren Marilyn Monroe and singer Annie Lennox, Prof Greenberg said.

"She has always been a loner; never really had close friendships," he said.

The court did not hear any suggestion the woman had dressed up during any of the alleged abuse.

The court heard CJ had experienced a series of problematic sexual relationships, falling pregnant when aged 13 and at 19 being intimate with a 14-year-old boy.

The trial before Judge John Williams continues.