Jahnessa Jerome was still holding the knife when she was confronted by police and arrested on her Johanson Cres balcony on October 6.

Her 45-year-old victim, a protected person under an apprehended violence order between the couple, was left with a life-threatening injury after the final of three unprovoked strikes pierced his lung.

The pair had been watching television inside the unit before Jerome struck the screen with a metal bar, picked up a bone-handled knife and stabbed her still-seated boyfriend in the upper leg.

The man went outside and flagged down a passer-by, who went to get first aid supplies. He returned to the unit only for Jerome to stab him twice more, in the arm and ribcage.

Jerome faced sentencing before Judge Andrew Haesler in Wollongong District Court on Tuesday.

The court heard the 27-year-old had developed an addiction to drugs in her late-teens and was homeless from the age of 19.

Her early home life was "disruptive" and her mother's boyfriend had once stabbed her mother, the court heard.

She began showing signs of schizophrenia only a year or two ago and only began seeing a psychiatrist once she went into custody, the court heard.

A psychiatrist had since diagnosed her with schizophrenia and substance use disorder.

"It would appear both were in operation at the time of the commission of the offence. It is clear that she wasn't able to think clearly or rationally, for there is no clear or rational reason advanced for the commission of this offence," Judge Haesler said.

"[Her] history included her hearing voices which, by the time of these offences, appeared to be constant and continued to this day."

A Good Samaritan removed the injured man's bloodied jumper and applied pressure to the wound, under his armpit before paramedics arrived and rushed him to hospital.

Jerome retreated to her balcony with the knife, yelling and threatening to jump. Negotiations with police continued for about an hour until she surrendered.

Jerome was sentenced to three years' imprisonment, with a non-parole period of two years.

With time already served, Jerome will become eligible for parole on October 5 next year.

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