A mother whose teenage daughter descended into psychosis — killing animals, having visions and hearing voices — took her to a naturopath instead of a psychiatrist. The 14-year-old later killed 10-year-old Biddy Porter at a property in rural NSW on July 8, 2020.

Two weeks before the killing, the teenager had confessed to her mother she thought about killing people, including her parents, 'all the time'. The NSW Supreme Court found her not criminally responsible due to mental illness in 2021. Two psychiatrists said she had schizophrenia and was in acute psychosis at the time.

The inquest, before NSW State Coroner Teresa O'Sullivan, heard disturbing details of the girl's worsening mental health. She slaughtered six chickens on the family property in June 2019. Her parents removed her bedroom door and snapped a video game in half as punishment.

When asked why she didn't seek mental health support instead, the mother said it didn't occur to her. 'Mental health was never on my radar,' she told the inquest on Wednesday. '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 chicken killings because the girl didn't have permission to slaughter the spent hens, which were due to be culled. 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 she consult a doctor after the girl revealed she had intrusive thoughts about killing people.

A GP wrote a referral for a psychiatrist in Sydney. The mother found it 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 farmhouse.

Biddy is remembered as a vibrant, clever and creative child who died of multiple injuries during school holidays. Her killer can't be identified for legal reasons.

The teenager's maternal grandmother said she was alarmed when she heard about the chicken slaughter 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.'

The mother said she hoped Biddy's parents found peace after the inquest. She described the loss of both Biddy and her daughter, who is in custody, as heartbreaking. 'My only regret is that I couldn't get more help for (the teenager) or have more understanding about mental health.'

Counsel assisting Peggy Dwyer, SC, said the coroners court wasn't an arena for blame or shame, but to find out what happened so counsellors, GPs and families can learn about mental health. The inquest has been told onset of schizophrenia in a young teen is extremely rare.

The inquest continues.

'My only regret is that I couldn't get more help for (the teenager) or have more understanding about mental health.'

If you or someone you know needs support, contact Lifeline on 13 11 14 or Kids Helpline on 1800 551 800.