Dark-haired Andrea Gordon believed her boyfriend was unfaithful with a hotel college catering student so she attacked her teenage rival.
It happened in a pub disco called Fawlty's in Killybegs.
Donegal District Court heard yesterday (Wednesday) how 20-year-old Andrea Gordon was driven by a text message about the new relationship to attack slightly-built 18-year-old Cassie Hanlon.
It meant a cell for Gordon who was remanded in custody to Ballyshannon District Court tomorrow so Judge Kevin Kilrane can decide on a penalty.
The court heard that on November 13th 2009 Hanlon, a first year student at the college in Killybegs, was approached by Gordon over a relationship with her boyfriend.
Garda Paul McCrossan said there was a fight. He added: "Andrea Gordon pulled her hair and pulled her down. It lasted quite a time."
The boyfriend later returned to his relationship with Gordon who admitted assaulting Hanlon and causing her harm.
The court heard from Hanlon's mother Ann that she suffered psychologically and was undergoing treatment. The family, including her two brothers, were very worried about her.
She no longer had a social life and her confidence had suffered.
Mrs Hanlon added: "She is not able to go out on her own.
"We don't want to see anything happen to her attacker so long as she acknowledges what she had done and won't do it to anybody else."
Gordon, of Lislaur, Riverstown, Co. Sligo, said in the witness box that she carried out a "random act" and she wasn't really like that. She added: "I had a lot of drink and there were the emotional effects of her being with my boyfriend."
She issued a public apology to her victim and her family.
Defence solicitor Eddie Henry said Gordon was on anti-depressant tablets at the time. He said: "The trigger was her boyfriend with this other person."
Prosecuting Inspector David Kelly observed that the victim was slightly-built.
Judge Kilrane said someone had texted Gordon about her boyfriend's new relationship and it upset her so she carried out a vicious assault in a disco.
He remanded her in custody to Ballyshannon court tomorrow (Friday).