The victim had recovered from her injuries, the court heard, but still suffered pain in her shoulder and stomach where she had been stabbed.
"The injuries were not life-threatening but that was a matter of good fortune," the judge said.
"Attacking someone else to the neck or the head carries with it the risk of serious, if not fatal injuries."
Williams' partner had been sleeping in the kitchen of the boarding house and on January 27, after consuming drugs and alcohol, she turned up to find him.
The victim, who lived on the upper floor of the building, was walking with a crutch after knee surgery and had just had a hernia operation at the time, the court heard.
She was playing games on her cellphone with her boyfriend in her bedroom when Williams knocked at the door.
The victim told her to leave several times, eventually punching her in the body and face when she refused.
Though Williams did not retaliate, the noise of the incident prompted her boyfriend to climb the stairs and intervene.
He went down to the street and began damaging the victim's car, yelling abuse as he did so.
While the woman and her partner also went outside, Williams diverted to the kitchen.
There she retrieved a black-handled paring knife.
The victim was only warned of her approach by a torrent of swearing.
Williams inflicted the three wounds using a "punching motion", the police summary said.
The victim's partner reacted by dragging the defendant down by her hair and shouting at her to release the knife.
When she refused, he grabbed at the blade several times, causing injuries to his hand in the process.
Police arrived at the bloody scene shortly afterwards and Williams admitted she had wielded the kitchen knife.
"I did stab her because I don't want a fight," she said.
"I was defending myself. I feared for my life. She's a horrible lady."
Although defence counsel David More accepted he could not argue provocation, he stressed the wounding would not have happened had the initial assault not taken place.
He told the court Williams had a 1-month-old baby and urged the judge to "temper justice with mercy" and stop short of a custodial sentence.
Judge Turner acknowledged imprisonment with her child (in a special mothers' unit in Christchurch Women's Prison) or without would make the sentence more arduous.
He also gave Williams credit for her attempts to leave her "chaotic" lifestyle behind.
However, it was not enough to result in having an electronically monitored sentence imposed.