How to convince get help for the sake of our relationship?

Am a 20 yr old girl and my girlfriend is 42 ,I posted a question 2 days ago explaining how my girlfriend hit me after verbally insulting her mom and getting in a fight w/ her afterward, and I said that am willing to call it a one time incident if she promises me not to lay a hand on me again. However she talked to me today and didn’t really apologize or promise anything,on the contrary she told me how my behavior embarrassed her and how I was being insensitive not caring bout her image in front of her old parents 60+, and just when I told her that she physically abused me .she told me that what goes up must come down ! and that I verbally abused her “defenseless” mom so I got what I was asking for :S. and that if I act like a brat I get treated like one, I told her how I cant tolerate physical abuse and she told me to “get over it , its not like I slapped your face or broke your nose”. she is acting like am making a big deal of it and that I should be sorry for what I did , and so I honestly didn’t feel like she understands just how much what she did was wrong she doesn’t even consider it abuse. my question is ; do you by any chance get her point and think she is right ? and also same old question how on earth am I to make her promise me not to do that again.and get help to control her temper?, this is serious. thanks.