A mentally ill woman who had two babies taken from her shortly after birth drowned her third child in the bath "to get rid of the evil in her", a judge has been told.
The 37-year-old woman, who cannot be named, pleaded not guilty on Monday to murdering her two-year-old daughter in their southwestern Sydney home in September 2016.
Her partner, who did not live at the address, told police that in the lead-up to the drowning she became paranoid, believed a ghost was in the house, said she was receiving messages from the TV and read the Bible to the toddler.
In the NSW Supreme Court, crown prosecutor Jose Crespo told Acting Justice Peter Hidden - who heard the trial without a jury - there was no issue that it was the mother who caused the child's death.
The issue was whether the evidence demonstrated she was not guilty of murder on the grounds of mental illness.
The toddler's body was found when emergency workers went to the house after concerns were raised by a family friend, while the mother was found to be in hospital.
She was seen driving erratically before she was involved in an accident, after which she asked police at the scene if they believed in God.
A doctor said her presentation was consistent with a relapse of a psychiatric condition involving schizophrenia, paranoid and religious thinking and non-compliance with medication.
She had had two other children who were adopted out, after authorities took them away from her shortly after birth.
Detective Senior Constable Brendon Barsic testified that the woman told him she had drowned the child because "she was trying to remove a demon from her daughter".
"She indicated she placed a white towel over her body before leaving the premises," he said.
She told him that over the last few days she had seen what the world really was like, that there was a lot of bad in it and she repeatedly spoke of "evil being present in the child".
A friend told police the woman said her daughter was evil and "had an old soul that needed to be removed".
Both Mr Crespo and defence barrister Janet Manuell SC referred to "voluminous" medical records showing the woman's long history of mental health issues and treatment.
The judge will deliver his verdict on November 23.
