Key Points:

Health officials have apologised to the family of a depressed Auckland mother who committed suicide while in the care of a mental health unit.

Brenda Moore, a 42-year-old social worker, was found dead on December 14 in the grounds of the Henry Bennett Centre at Waikato Hospital, Hamilton.

Donna Moore, a doctor's receptionist in Auckland, says her sister's death has "destroyed us as a family".

She is demanding to know how her sister could go missing when she was meant to be under supervision, and has complained to the Health and Disability Commission.

It's another embarrassment for the country's mental health services after two patients under the care of Wellington's Crisis Assessment Treatment Team committed suicide in the past three months.

The Waikato District Health Board is investigating Brenda Moore's death and reviewing policies and procedures.

Mental health and addictions service clinical services director Dr Rajiv Singh offered his "deepest condolences to all involved in her care".

The mother-of-one worked for years with children at Middlemore Hospital but most recently was at Thames Hospital. Last August, she sought help after complaining of burnout, depression, relationship issues and exhaustion.

In November, Brenda Moore became a voluntary patient under the Mental Health Act because she knew she was a danger to herself. She knew she should be put into care for at least five days, which would have given her time to get well.

Donna Moore says two days later Brenda was sent home by a doctor and told she could catch a bus, about which the board refused to comment.

On December 11, Brenda tried to take her life and was taken to Thames Hospital where she was sectioned. The following day she was taken to the Henry Bennett Centre.

"We believed she was safe for five days and then we could think about how to help her," said Donna.

Brenda disappeared on December 13. Singh said the ward and grounds were searched. Her body was found 25 hours later by a member of the public.

Singh said patients were safe at the centre. The incidence of successful suicides in an inpatient ward was "extremely low. We make every attempt to minimise the risk, but certain events are beyond our control."

An inquest was to be held this month and in the meantime, Brenda's family had an open invitation to meet staff.

Coromandel MP Sandra Goudie said Brenda Moore's care was "grossly incompetent". Goudie said her death was a tragedy because she had been told Brenda was one of the "best social workers in the business".

Donna said she would seek Government answers. "I want procedures in place so this will not happen again."