My daughter knew that something wasn't right. AW started what I would call her "problem drinking" when Daughter was about 15. I knew AW was an alcoholic by then, but Daughter would kind of giggle with embarrassment and say "Mom's sleepy".
After AW fell a few times, daughter kind of figured it out, and we talked about it. She still wont' admit that AW is an alcoholic, though. I suppose that denial gives her a little bit of comfort.