I understand what you're saying. Couple of weeks ago I was walking around the neighborhood and my friends met up with this girl for her birthday party. Her mother was saying some weird **bleep**, and then the girl started cursing her out. I was going to tell her to shutup because it's disrespectful, but then the mother started saying racial slurs, stumbling, she even grabbed me and kissed me on the cheek. It was REALLY embarassing for her and her mother, and I felt bad. Make sure she doesn't drink..or record her when she is drunk and show her how stupid she is when she gets drunk -- that might cause her to slow down.
Even if she does get drunk she's still your mom. My dad was an alchoholic but I never said I hated him and now he's been sober for like 3 or 4 years now. So, she can change her habits if she tries, you just gotta support her.