A woman who slammed Louise O'Brien's head through a glass pane later put a Band-Aid on the teen's head wound and "told her to get over it", Wollongong District Court heard on Friday.
The woman's daughter told the court the assault accounted for the mismatched glass panes on the front door of the northern suburbs house where Louise had been living with the woman - a family friend - and her children.
Louise died soon afterwards, from injuries that have been the subject of separate court action.
The woman was yesterday found guilty of three charges of assault occasioning actual bodily and a charge of common assault. She was acquitted of a second charge of common assault.
On the day the glass door pane was destroyed, the offender had been arguing with Louise and "ended up grabbing Louise by the head and slamming her head through the glass", the witness said.
"[Louise] got cut on the top of her head ... a deep cut above her eyebrow. There was a lot of blood coming from it," she said.
"Mum put a Band-Aid on it and told her to get over it."
The witness told the court her mother then telephoned the Housing Commission to ask that the door be repaired, claiming the damage was the result of a failed break-in.
When a worker arrived to carry out repairs, "Louise was in the back bedroom. Whenever anyone turned up she'd be put in the back bedroom so nobody could see her".
Defence barrister Wayne Flynn asked if there was tension between the women's children and Louise because Louise "got to go everywhere" with the woman.
Mr Flynn: "The fact is that all of your brothers and sisters and you hated Louise, was that correct?"
The witness: "No."
Did you tell police all of your brothers and sisters hated her because she got to go everywhere with your mother? - I said everyone sort of disliked her for that.
Including you? - Occasionally, yes.
And that often ended in physical fights between the children that lived in the house and Louise, isn't that correct? - Not all the time.
But [often]? - Yes.
Judge David Frearson adjourned sentencing to Downing Centre Local Court on March 21, because of the woman's medical issues.