Two weeks after the 14-year-old confessed to her mother she thought about killing people, including her parents, "all the time", the girl killed 10-year-old Biddy Porter at a property in rural NSW.
Biddy, remembered as a vibrant, clever and creative child, died of multiple injuries while staying at the property in the school holidays on July 8, 2020.
The NSW Supreme Court found Biddy's killer, who cannot be identified for legal reasons, was not criminally responsible due to mental illness in 2021.
Two psychiatrists found the teenager had schizophrenia and was in acute psychosis at the time of the killing.
Counsel assisting Peggy Dwyer SC told the inquest of the teenager's worsening mental health before the killing and "disturbing" signs of psychosis, including hallucinations and a sense of not feeling real.
After the teenager slaughtered six chickens on the family property in June 2019, her parents removed her bedroom door and snapped a video game in half.
When asked why she did not seek mental health support for her daughter instead, the teenager's mother said it did not occur to her.
"Mental health was never on my radar," the mother told the inquest on Wednesday morning.
"I never believed in mental health, I didn't understand mental health so it didn't come up to me as something I needed to do."
The mother insisted she was only upset about the teenager killing the animals because she did not have permission to slaughter the spent hens, which were due to be culled.
The mother did not consider the incident a "red flag".
She told the inquest she took her concerns to a naturopathic herbalist, who advised the teenager to take magnesium.
"The reason I spoke to my naturopath was I thought there was a hormonal imbalance in (her)," the mother said.
The naturopath later suggested the mother consult a doctor after the girl revealed she had intrusive thoughts about killing people.
A GP wrote a referral for a psychiatrist in Sydney, which the mother found in her email spam folder only after the first day of the inquest.
One week after the GP appointment, the teenager killed Biddy while the two were left alone in the farm house.
The mother said she hoped Biddy's parents found peace after the inquest.
She said the loss of both Biddy and her daughter, who is in custody, was heartbreaking.
"My only regret is that I couldn't get more help for (the teenager) or have more understanding about mental health."
The teenager's maternal grandmother said she was alarmed when she heard about the slaughter of the chickens and urged the mother to seek psychiatric help.
"That was a little girl in crisis," the grandmother told the inquest.
"The crisis was the fact she was extremely mentally disturbed, something had gone very wrong."
Dr Dwyer said the coroners court was not an arena for blame or shame, but rather to find out what happened to Biddy so counsellors, GPs and families can learn about mental health.
Onset of schizophrenia in a young teen is extremely rare, the inquest has been told.
The inquest continues before NSW State Coroner Teresa O'Sullivan.
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