Donella Knox supporters plan protest against her incarceration

A close friend of Donella Knox is organising protests across New Zealand to highlight Knox's incarceration and the organisations she says failed to help her.

Last year, Knox murdered her severely disabled and violent daughter.

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 friend, Sharna Butcher, says the case is a tragedy.

"The main thing New Zealanders need to know is that Donella is not a murderer; if anything it was a type of euthanasia," she says.

"She didn't want to see Ruby suffering. She was the most beautiful, compassionate, empathetic, loving person and mother."

Ms Butcher is organising marches in major city centres to coincide with Autism Awareness Week, which runs from April 3 to April 7. She is also planning a petition to take to Parliament.

She says Knox was put in an intolerable position, and support organisations failed to effectively coordinate to deliver the care needed.

"We would try and help her look after Ruby, but we would be attacked and she would try ripping our throats out," she says.

"She was obviously in pain and suffering, and it was hard for all of us as well, trying to help her get some sleep when we couldn't handle Ruby with her size."

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.

"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," lawyer Simon Shamy says.

At Knox's sentencing, High Court Justice Joe Williams acknowledged she faced a difficult, stressful and dangerous job caring for her daughter, and accepted Knox felt let down by the health system and that she had run out of options.