Most Helpful Girl
Partying or getting drunk doesn't automatically make someone a bad person. Are you sure you're not just jealous and overreacting?
It doesn't really matter if they're good or not though, you should really stay out of it unless you think her life is in actual danger. Going through this kind of stage can be good for some people, it might help them realize what kind of person they actually want to be with. Some people need to make mistakes in order to learn, and that's ok as long as they actually don't hurt themselves too badly and get into some serious trouble. So yeah, stay out of it unless you actually think she's in danger.