A woman who showered and dressed her young son after stabbing him 29 times has had her sentence cut due to her psychotic state at the time of the attack.

The now 35-year-old woman checked her autistic son and daughter into a hotel in western Sydney in February 2022, telling them they "had to be in heaven so the bad ladies couldn't take them away".

The following morning, during a psychotic episode at the Nesuto Parramatta Apartment Hotel, she used a kitchen knife to stab the nine-year-old boy 29 times in his neck, torso, chest, arms and thigh.

She showered and dressed him, before bundling both children into her car, which she deliberately crashed into posts on the side of the M4 motorway.

Her son was taken to Westmead Hospital and survived after emergency surgery.

The woman - who cannot be legally identified - was sentenced in November 2023 to nine years and six months in jail after pleading guilty to one count of wounding with intent to murder.

"The voice told me I needed to do it now with the knife so my children were safe," she testified during the sentence hearing.

"(The bad ladies) were going to drag them out of the hotel by their hair and give them to their father and they'll be raped over and over and over again."

On Wednesday, she reduced her maximum sentence to five years and six months after the NSW Court of Criminal Appeal found the jail time originally imposed was manifestly excessive.

Her new, three-year non-parole period expired on February 12, 2025 and she will be immediately eligible for release.

Justice Sarah McNaughton said the overriding factor in the case was the woman's acute psychotic state when she stabbed her son.

"This level of acute mental illness was found by the sentencing judge to have impacted the applicant's moral culpability and objective seriousness of the offence," she wrote in a judgment accepted by two other appeal judges.

However, these findings were not reflected in the excessive sentence originally imposed in November 2023, Justice McNaughton added.

The judge accepted the woman had undiagnosed schizophrenia, although she was taking anti-psychotics.

She also noted the 35-year-old's insight into her illness and her remorse while acknowledging the need to punish her for breaching the trust between a parent and child.

The woman also pleaded guilty to one count of perverting the course of justice during a phone call to her mother from Silverwater prison in August 2022.

"You gotta tell (my son) to tell police that it wasn't me who's hurt him," she said at the time.

"Because otherwise I could be in (jail) for 10 years or something."

In September 2021, she alleged to police her son had been sexually assaulted eight months earlier by his father, from whom she was separated at the time.

After the NSW Department of Communities and Justice became involved, the woman became distressed and paranoid, fearing her children would be taken away from her.

In February 2021, she told police her ex-husband had made phone calls threatening to kill her and the children, and that she had to move into temporary accommodation.

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