Hogg, 29, said the sentence implied that Ruby's life was "worth less simply because she was severely disabled".
"The sentence of four years in [jail] for the murder of Ruby is nowhere [near] enough," she said.
She said Knox wrote in a book which she self-published a month before killing Ruby that she had thoughts of hurting Ruby and "blowing up the hospital".
"Why did no one who read that book go to the police, or go to the Ministry of Health Disability Support Services, to show Ruby's life was at serious risk?" she asked.
"Why did the local district health board not investigate earlier and thoroughly why Ruby was in horrible pain leading to lashing out to others in her life? Where was the pain management team?
"Where was the crisis management support team to sort out Ruby's increasing behavioural issues? Where were they in investigating the cause of Ruby's pain and alleviating Ruby's pain by pain medication or any number of health tests that could have been done to get to the leading cause of Ruby's increase in behavioural issues?
"The fact remains that there is actually no crisis behaviour support for autistic individuals going into crisis."
Hogg said Donella Knox "likely needed to give Ruby up so both of them could be safe".
Another woman who was born physically crippled, Rachael Goldsmith, said she was almost killed by her mother at age 8.
"She came into the bathroom saying she was wanting to wash my hair, and held me under the water till I passed out," she said.
Her mother had mental health issues and Goldsmith was eventually placed into foster care at age 15.
Dr Esther Woodbury of the Disabled Persons Assembly disputed the judge's statement that the Knox case was "once in a generation".
"Disabled children are killed by their parents quite frequently," she said.
She said prison was not a good answer for many prisoners with mental and physical impairments, and it would not help anyone for Knox to be jailed either.
"On the other hand I think there is a great danger of the deaths of disabled people not being treated similarly to the deaths of non-disabled people," she said.
Autism NZ chief executive Dane Dougan said there was a lack of training about autism for both caregivers and teachers.
"We are hearing of more and more families not wanting to use carers because they don't know how to interact with kids with autism and potentially make things worse," he said.
"We believe that can be improved because the training is not there."
Former Autism NZ president Wendy Duff said she hoped the protest marches would raise awareness of the need for more specialised support for people on the autistic spectrum.
"When the behaviours become unmanageable and the child or young person needs to go to a safe house, it's not there, because they can't go into a shared respite space because they are too challenging," she said.
Robyn Shearer of the mental health and disability workforce agency Te Pou said her agency spent $4 million a year on training grants for the 20,000 people caring for disabled people.
"The great challenge is that large numbers of workers are not always skilled, or even have basic literacy some of them, and that is because of the quite low pay rates," she said. "You are not going to attract people to work in an area that requires quite a lot of skills when you are on the minimum wage."
