I'll pile on with the recommendation for Al-Anon. It is truly a lifesaver for anyone whose life is profoundly affected by someone else's drinking.
I also strongly suggest that (maybe even before you have a talk with her) you educate yourself a bit about alcoholism. There are a lot of misconceptions floating around out there. I recommend that you read a book called "Under the Influence" (excerpts are available
here. Another good read is the AA Big Book (especially the first 164 pages). You can read the Big Book online
here.
Doesn't hurt to know what you're dealing with.
Welcome, glad you're here.