The inquest decision, much of which was suppressed, noted that Child, Youth and Family had admitted failing the girl, who took her own life while in foster care after she claimed to have been sexually abused by a caregiver. She was found dead in her bedroom by her younger sister at their foster home on September 13, 2008.
She was one of eight children from a Northland family placed in CYF custody in 2006, after their parents were arrested on drugs charges. The placement lasted until 2008, when she claimed that she had been sexually abused and they were moved.
The girl killed herself after being sent to her room for fighting with her sister and being told she would not be allowed to stay if her behaviour continued, the coroner's finding added.
It also heavily criticised the social welfare system for a series of failings by social workers after the sexual abuse claim was made.
Coroner Morag McDowell said the new caregiver, who had been looking after her for only three weeks, had not been properly informed of the child's fragile mental state. Not did the girl receive the counselling or psychological support required.
Coroner McDowell outlined a number of "missed opportunities" to manage the girl's fragile mental state, and expressed particular concern over the care plan given to her new caregiver, which was out of date and lacked detail about her individual needs and personal history.
"Ensuring that those people taking over the parental duties of a child have all the necessary information needed to provide adequate support tailored to that particular child is fundamental," Coroner McDowell said.
CYF fully accepted the coroner's findings. The social worker who had produced the sub-standard care plan left the agency soon afterwards, while another social worker involved in the case had received extra training.
"Put simply, we failed (the child)," deputy chief social worker Nova Salomen said, adding that "big changes" had been made in the way it worked with abused children in a bid to prevent such a failure in the future.
It had strengthened its care plans to improve key information provided to caregivers, and implemented a specific assessment tool for social workers working with children over the age of 12. Changes had also been made to information systems for social workers to highlight suicide risk and critical risk checks.
Gateway assessments were now being used to assess the wider needs of all children in care, and the scoring on those tests had been automated to remove the risk of human error.
CYF apologised to the child's family for its failures, Ms Salomen added.
"We agree with the coroner that this case is a reminder for social workers to focus on the needs of children rather than being process-focused," she said.