I think if you're worried you should inform your parents of what's going on with her - then it's best to leave it to them to decide what to do. You can't take responsibility for her actions or their consequences. It's just not your place. We can't make anyone see or do anything they don't want to. Focus on your own life and these feelings of anger and jealousy within therapy. Continue to work hard so eventually you can move out and lead your own life.

Siblings aren't the be all and end all - you might not have much of a relationship with her when you're older or the reverse might be true. But it's not uncommon and just because people are related to us it doesn't mean we're obliged to get on with them or involve ourselves in their business either.

Reconfigure your priorities and realize that this situation won't stay the same forever - if your sister wants to be reckless then one way or another she'll have to reap the consequences. All you can do is be a supportive where necessary and failing that - get on with your own life.