I would be willing to bet the bulimia is a symptom rather than a cause of whatever the real problem is. I would not address that specifically as I think it could make her feel defensive and/or guilty—instead, try to find out what’s going on in her life that could make her so unhappy. And this is one for the pros. Eating disorders are, sadly, extremely difficult to treat. I would not try to do this on your own. I would seek out the advice of a competent therapist who specializes in eating disorders before talking to your daughter, ideally. And in general, try to be gentle, understanding, supportive, and most of all, nonjudgmental.