Shannon Balshaw, 21, of Maple Crescent, Preston, attacked two women after urinating on the floor of the ladies lavatories in Preston's Evoque nightclub.
Preston Magistrates' Court was told Balshaw took exception when the victim and her friend, who were putting on their lip gloss, told Balshaw: "That's not the toilet hun."
She then grabbed the woman's head and pulled her towards the floor, ripping out a clump of hair.
The second woman went to assist her friend and was pushed, and also grabbed by her hair.
The court heard as the first victim got up she felt a sharp pain and realised there was a lot of blood was coming from her nipple.
Medics at Royal Preston Hospital told her she could 'lose her nipple', but it was repaired in theatre, though she has been left with scarring and asymmetrical nipples.
She also had to have a hepatitis C jab.
Balshaw began to cry in the dock as the woman's victim statement was read, in which she said: " I feel like I've been put back mentally and physically. It will take me a while to get back to how I was.
"I wondered how am I going to look, will I be able to breast feed?
"It's such a life changing injury for a young person like me."
She added she felt "embarrassed and ashamed" of the scar, had become "anxious and jumpy", and had missed a holiday to Magaluf due to medical advice.
Balshaw, who was subject to a community order for a racist assault in Roosterz Chicken, Preston, last April, at the time, denied the offences and cited self defence.
But she was found guilty of causing actual bodily harm to the first woman, and assaulting her friend, after a trial.
Defending, Jon Lee said the magistrates had accepted there was a 'squaring up' between Balshaw and the victims' friend in the toilet, and argued the defendant had been pinned to the floor by the women.
He added: "The defendant has always accepted she bit her. What she was saying is it she was in a toilet being set upon by two females - one holding onto her legs - and the only thing she could move was her face.
"She accepted the only thing she could do was bite and at first she bite her on the arm. She never meant to bite her on the breast - but she did intend to bite her.
" Nothing in the medical evidence seems to suggest it was 'hanging off' - it's a puncture wound.
He said her extreme reaction may have been due to previously being a victim of horrific domestic violence.
The chairman of the bench said: "Due to the harm caused and your previous violent offences - two of which are racially aggravated - we've decided we will be committing this case to the Crown Court.
"We have insufficient powers here to deal with you."
She will next appear on October 21 and was granted unconditional bail in the meantime.