We were in deep conversation with a couple once when the subject of another couple came up and how the lady had been rude to me one night at the club because she was drunk and that she sent me an apology via message. I mentionned that it's too bad she is always wasted or things like this would not happen and they defended her by saying that she is a mother and works hard and you can't blame her for letting her hair down and partying a bit when going out for the night. Nope, you sure can't, only problem is that we've never seen this lady sober, ever!
Our advice, tell her straight out that her excessive drinking makes it hard for you to take get it on with her since you are too nice of a person to take advantage of a drunk person. It's cheesy I know, but it may just work.