trying to help my angry alcoholic drug abusing sister. PLEASE HELP.?

my 18 year old sister is a severe alcoholic. i know she uses drugs, but i am not sure of what kind and how often. she is living with her boyfriend who has been to many different rehabs across the country and either gets kicked out or just leaves the program. he was addicted to intravenous heroin and alcohol. and is exceedingly wealthy and pays for all the drugs and alcohol, he is an ultimate enabler. he tells her that i am a liar and that i am trying to control her life by trying to help her, and that i am really not trying to help her at all. they hang out with two guys that the boyfriend met in rehab who have relapsed. my sister just got out of jail for putting a ciggarette out on her boyfriends neck and for punching him repeatedly in the face resulting in a black eye. someone that was in the house called the cops on them, and the boyfriend wouldnt press charges. i tried to pick her up from the jail and the boyfriend lied to me about what time she was getting out so i couldnt. i was going to try to have an “informal intervention” with her. i am at a loss. she was completely un phased by this experience, and is always un phased by the catastrophes that come from her addiction. i just recently found out that she was date raped by an acquaintance who house she was couch surfing at awhile ago, and my mother says that she fears that, that wasnt the first time she was date raped. she is showing signs of jaundice and is sick alot of the time. she can not control herself. this time it was a cigarette but maybe next time it will be a knife, and i am terrified and feel nauseous and overwhelmed from trying to help her. she has been stealing money from me and i just dont know what to do! i have been searching online for hours trying to think of something.
she is also the most avoident person there is. please any advice will greatly help!

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