Only 3 questions! (SPOILERS)

If you're talking about the real Christiane...
It's not exactly her mother didn't care much, she just had to work a lot and was focused on her new relation with the young guy that appeared in the movie, but after she discovers Christiane's addiction, she actually made a lot of things and efforts to help her... But Christiane just kept relapsing until she is send to live with her grandmother (sended by her mom in a last effort to get her clean) and that's when she quit heroin... At least for some years... That's where the movie ended, but they did not showed off all the things the mother did to help Christiane...
2. No, her sister didn't died from drugs, in fact she is still alive also and got an interview some years ago... I remember she stated that she actually tried some drugs but never heroin or hard stuff, because she didn't want to end up like her sister. Althought in the film the sister's name is Sabine, that's not her real name.
3. Yes, Real Christiane and real Detlev met again in adulthood, in fact there is a small writting from Christiane telling about this encounter, she says that they were totally different persons and got anything in common by the days they met again, and that Detlev was in the brink of death again when she was clean... Some sources state that real Detlev died soon after from and overdose and others state that he managed to get clean and by now he got a wife and son. I don't know which one is the truth.