If she is an abuse victim then she is following a very familiar pattern that's common with lots of abuse victims, which is to create a situation where she can take out her anger, pain and hurt on society in general and on those closest to her who she will subconsciously feel should have protected her. This will include things which can blot out pain, so drink and drugs are very common. The first thing your friend needs to do is understand that given the situaiton this is all very normal ( fraught though it may be) and that with careful help it can be addressed. Social services are quite right she can't just 'put her in care' and whyever would she want to this is her child, who is suffering and needs support? Social services can however arrange other things to help, therapy, counselling etc.
The first thing that needs to happen is that dialogue needs to be opened up and the talking needs to be honest, it's no good glossing over what happened and thinking that it's better buried befause this is rarely the case. There are I believe family counselling sessions and it's vital this is addressed as not addressing it cna lead to a lifetime of trouble hurt and dysfunction. I'm speaking form first hand experience, I screwed my life up because no-one helped me to deal with the way I was feeling after my father physically abused me and my mother turned a blind eye and it took me into my 30's to regain anything of myself ( thanks to my then wife). I would hate to see this happen to this young girl, so please advise your friend to help her and not to simply try to find a way of normalizing her straight away because that really won't happen and she'sll just feel more and more isolated.