Donella Knox's murder of autistic daughter 'a perfect storm'

The circumstances leading up to a Blenheim mother murdering her severely disabled daughter have been called a "perfect storm".

Donella Knox's lawyer says she felt desperate about the lack of social and specialist help available to help care for her severely autistic and intellectually disabled daughter Ruby.

At age 10, Ruby already weighed 74 kg. But as she grew physically, her mental development stalled. She couldn't communicate, was violent and needed constant care.

In May 2016, Knox gave Ruby sedatives then suffocated her. In December she was sentenced to four years in jail, with court suppressions meaning details of the case could only be reported on Friday.

Knox's lawyer Simon Shamy says the case highlighted the state of desperation she was in after caring for Ruby on her own for 20 years.

"This is something where Donella as a mother did everything humanly possible for Ruby for 20 gruelling and isolating years, and basically at the end of it she had nothing more she could give."

Mr Shamy wants more support for families and full-time caregivers of severely disabled children, and says they should be paid more.

"Requiring intensive, every-minute-of-the-day supervision, like Ruby - who was prone to find knives and cut herself, to drink Janola or to put her hand through a window - that deserves payment."

Ruby Knox
Ruby as a child (File)

At Knox's sentencing, High Court Justice Joe Williams acknowledged she faced a difficult, stressful and dangerous job caring for her daughter.

"She would pull hair, head butt, scratch other children," Justice Williams said. "She would attack animals and you."

Health professionals said she had been adequately supported - and had received more assistance than anyone in Marlborough.

But Justice Williams accepted Knox felt let down by the health system and that she had run out of options.

He acknowledged Knox's constant, unselfish and unconditional love for her daughter.

A previous version of this article stated Donella Knox was being paid $75 a day to care for her daughter - this was incorrect and has been removed.