Rebecca Butterfield's last jail sentence - for a jailhouse homicide - expired in November 2015 but she's been held ever since due to her unacceptable risk of committing further serious offences.

NSW Supreme Court Justice Robert Allan Hulme this week extended her continuing detention order until November 2023, saying the 46-year-old had a history of "sudden and unprovoked violence".

"There is little to indicate that this risk has dissipated to any significant degree in more recent years, or that it is likely to do so for the foreseeable future," he said.

"Nothing appears to have changed in relation to Ms Butterfield's predilection for sharp objects when available. Her outbursts of violence can be unpredictable in that they are not responsive to anything that is rationally and objectively provocative.

"They can be constituted by acts which have occurred suddenly with no or little forethought of the consequences. They are indicative of an inability to restrain or regulate her behaviour. Without intervention and restraint being immediately available, the consequences can be extremely serious, perhaps even fatal."

Butterfield was convicted of manslaughter after stabbing a fellow prisoner 33 times with a kitchen knife in an unprovoked attack in 2003.

She was previously jailed for stabbing a taxi driver over a fare and stabbing a neighbour trying to stop her self-harming.

More recently, she attacked a doctor trying to administer local anaesthetic, attacked prison guards with hot tea and thrown hot water at an inmate.

"I will kill when I get out," she said on one of those occasions, the judge said.

Medical experts say she has antisocial and borderline personality disorders but were divided about whether she had schizophrenia.

Forensic psychiatrist Richard Furst, who treated Butterfield previously, questioned if hallucinations were made up.

He also concluded she was "one of the most dangerous women in Australia" and warned moving her to a forensic hospital would increase her access to potential weapons and victims.

But maintaining the status quo - which left Butterfield isolated and with limited access to therapeutic activities - would at best cause no improvement in her condition, current treating psychiatrist Natasha Rae said.

"The worst case scenario (is) it would be so catastrophic for her in terms of losing all hope that her risk ... increase," Dr Rae said.

Justice Hulme noted Butterfield had been abused repeatedly as a child and her case was "sadly illustrative of the lasting trauma and terrible consequences of (violent) offending".

But he refused to make a special order to allow Butterfield to request transfer to a forensic hospital.

"There is no question that she continues to pose an unacceptable risk of harming herself and members of the community, including staff, inmates and patients of custodial and medical facilities."

Butterfield may still end up in a forensic hospital.

Under new mental health laws expected to come into force this year, Corrective Services will be able to transfer prisoners held on detention orders to mental health facilities.

Australian Associated Press