I'm sorry about your niece too
unless someone is starting to realize they have a problem, there's precious little you can do I'm afraid. Just be her friend I guess, maybe try to find out why she drinks so much. The risk is she'll think you're interfering and yep, tell you to get lost, so go carefully now. On the bright side, a lot of people go through a phase of getting wasted all the time, and a lot of em grow out of it eventually. That's what I'm trying to do now