A woman with an intellectual disability was regularly kept in isolation for 23 hours a day, a royal commission has been told.
A hearing of the Disability Royal Commission was told a traffic light system was used to manage behaviour at the forensic hospital where the woman, given the pseudonym Melanie, lives.
"Using a traffic light system to determine whether somebody gets to leave a very small space for a short period of time is not something that the Public Guardian has ever supported," NSW Public Guardian Megan Osborne said.
In an audio recording, Melanie said she had "stayed strong" despite sexual, physical and psychological abuse.
She lived with a number of different families and changed schools as a child, and commissioners were told she engaged in two "very serious" acts of violence as a teenager.
One resulted in the death of a staff member at the juvenile detention centre where she was being held and resulted in her transfer to an adult prison, counsel assisting Janice Crawford said.
She was found unfit to plead in relation to two acts, one of which related to manslaughter.
It was acknowledged she should not have been allowed to participate in an activity where she gained access to the weapon used, and the state of NSW entered a guilty plea to a breach of occupational health and safety, the hearing was told.
She left prison in 2011 when transferred to a forensic hospital.
Commissioners heard she has been kept in the hospital as a civil patient since 2012 when her limiting term, representing the custodial sentence imposed under typical circumstances, expired.
She has now been detained for more than 20 years and was moved to the seclusion area when her mental health deteriorated between 2012 and 2014.
"Not one day in my life that I didn't want to get out and have a life and be happy again on the ward," Melanie said.
"It was inhumane to keep someone locked up for that long in a seclusion area."
She lived in the isolated environment "almost constantly" for about seven years, until November 2020.
"Normally I wouldn't say I'm proud of myself ever. But everyone is proud of me so I'm proud of myself," she said after being transferred to a room on the ward.
Ms Osborne visited the area where Melanie was kept in isolation early last year.
"The feeling that I had visiting those seclusion rooms was one that I will never forget and will never leave me," she said.
"I felt quite anxious and overwhelmed and knew that I wouldn't do very well if I had to spend any period of time in those rooms."
She said Melanie's move to the ward was a step forward and she believed it happened a lot quicker after she fractured her foot while in isolation.
"My view would be that caring for Melanie in a moon boot would be very difficult in seclusion versus on the ward," she said.
An eight-day hearing of the Disability Royal Commission will hear from 33 witnesses as it explores indefinite detention and the "cycling in and out" of prison by people with disability.