My situation was a bit different, but hope it adds some depth. I'm a guy, and for two years in college I'd got wasted constantly, was mean most of the time, and I have some crazy stories, consequently. My friends couldn't, and still can't, understand how I was so mean when drunk because I'm nice the rest of the time. I was single then.
Finally I cut back, stopped drinking so much, and got a girlfriend. Still, I did get wasted at times, and I ended up cheating on my girlfriend a couple of times when I had been drinking. After that, I completely stopped. Went sober for 6 months, and now I only drink in moderation, and I really do mean that.
I was a mean drunk, but I wanted to change and did. If your gf really wants to change, then you should give her that chance, just know it will be difficult. If she's set in her way, then hit the road. But make it clear to her that her behavior is unacceptable.