My 15 y/o sister is struggling with addiction/abuse issues (ADVICE SERIOUSLY NEEDED)

Me and my sister couldn’t be more unalike. I’ve always been straight cut. Ive never rocked any boats or caused anyone any trouble, even at 20. Our 17 year old brother is the same way, so unproblematic it’s boring. My baby sister who’s only 15 is a drug addict, alcoholic, a kleptomaniac, she’s constantly running away and sneaking out, she’s contracted 3 STD’s in the past year, and worst of all she lied about getting raped when caught with a boy (confirmed and later admitted), etc.

We grew up in a supportive, happy, progressive, and endlessly loving family, although we grew up financially unstable and with a single mother, she’s ALWAYS provided us with the best opportunities and resources. There’s really no psychological or childhood explanation for my sisters actions.

We no longer know what to do with her. We’re all worried to death and we pretty much just don’t want her to die. We’ve been strict, but she just threatens to kill herself. We’ve been lenient, but then she takes advantage of us all. We’ve provided her sanctuary, therapy, meds, rehab, everything!! None of it works and I don’t know what to do. Her excuse is that she know what she’s doing, but doesn’t care and will never stop. I’m so stressed this has become my whole life. I can’t focus on classes, work, relationships, myself, etc. while she’s here.

What I was honestly wondering, has anyone here had experience with addiction or this behavior, and would you please be willing to provide advice?? I’ll take anything at this point. It’s putting so, so much stress on me and my family and anything helps. Thank you!!