I grew up with a father drinking 2 or 3 rum and cokes every single night. As an adult, with no inclination to drink every night, I realize how abnormal that is. When you have to try to ignore things, make a point of not telling people, when it's enough of a problem that you come looking for help on a forum, it's a problem.
You mentioned she seems to forget what she's done while drinking, and not knowing if she really forgot or not. My father recently asked me (yet again) why I'm upset with him. I gave him a looooong list of ugly things he has said and done to me over the years, the last of which was just the last straw. He told me I'm imagining it all. Including him throwing me on a bed and trying to choke me. I didn't even bother mentioning a crystal clear memory I've had since I was 4--too young to think up or imagine such a thing on my own--of sitting beside him in a dark movie theater watching what was at least soft porn. I know I'd be called a liar for saying that.
At this point, I understand that I can either continue trying to live in his make-believe world where we all pretend none of it happened, which means he can continue his abusive behavior and I can continue smiling and showing up for more abuse because, well, it's not really happening is it, so why would I possibly do anything other than smile and be pleasant? He gets to abuse and have a happy daughter, what a deal. Or I can walk away. There is absolutely no other choice when dealing with this sort of thing, until/unless they recognize there's a problem that THEY need to fix.
As Ginger said, you didn't cause it, you can't control it.
I also highly recommend al-anon. I only went 6 months but have gotten so much benefit from that time, in being able to pull away and work on my own life.