Unless her alcoholism and drinking is a "known" to your company, or there is some kind of policy forbidding the use of alcohol I would stay away from the subject completely. You could be opening yourself and your company up to a HUGE potential liability by approaching her about it. I'd personally keep your conversations focused on her work performance. If she's not meeting deadlines or completing work as she should be, then you could follow whatever guidelines are in place to get things back on track. But approaching here straight out about her alcoholism as a supervisor would be akin to you asking about personal medical details - off limits for sure.
If she were to ASK for help you could certainly direct her to any resources your company has or recommend she see a doctor for help, but you don't want to be in the middle of any of it. She could also turn against you - remember that active alcoholics don't think logically.