This is almost exactly what happened to my sister. Mum got drunk called herdisgustingpig and locked her out of the house so she couldn't use the toilet or anything. I went and picked her up and took her to my dads. She ended up living with an old school friends mum. 

I just thought, could it have just been a one off?

I say do what you can.

When your that age regardless of how great or how horrible your family is, you always think that nobody cares about you.

In her case if nobody helps her, she will grow up with that chip on her shoulder.

People  who grow up that way ultimitely have problems in later life when it comes to being responsible because they have the mindset 'society doesn't care about me, why should I care about society!'

That seems to be the main problem with the current youth mindset and associated problems we keep seeing.

Talk to her about it, find out how much of a problem her mother can be and maybe get her help with social services.

Also consider how serious your son is with her because doing nothing will effect your relationship with him.

People raising daughters really need to read 'RAISING GIRLS' by Steve Biddulph.

I think both of his books are a good guideline.

Here is his interview on ABC.

http://www.abc.net.au/classic/content/2013/02/13/3685524.htm

http://www.abc.net.au/cgi-bin/common/player_launch.pl?s=classic/classic&d=classic/program/midday/aud...

It is sad to hear advertising agencies used work and employed psycologists to work out which demographic was the easiest to exploit.

They worked it out as 8 year old girls.

Update!

We had the young lady in question over today and things were a little better.

She stayed last night at a friends place and she was planning to go back there tonight.

Her bio dad has told her she is welcome back to live with him any time she wants.  So she does have somewhere to go.

We sat together and had a chat this afternoon and she had a good cry.  Her mum has been a pain in the butt for the past 4 years which is why she moved out when she was in year nine.

Miss was hoping that things might have improved in the few years she was away but sadly NO.

At the last 2 highschools she was at she saw the school counsellor and got no real help from them.  Her mother even made the appt for her to see the first one saying that she was certain her daughter wasn't dealing with the break up of the parents marriage - that was 5 years after the break up and she explained to the counsellor that the end of her parents marriage wasn't the problem it was the abuse from her mother, both physical and verbal that was the problem and the counsellor said "Well that is not what your mum told me"  ?:|

So she is is no hurry to go back to see the school counsellor.  😞

Anyway she tells me she will only be staying there till she is 18 and then she will be gone.  But if things get too bad she will go to her dads.  It is not ideal but we can't make her move out.  It was sad listening to her, hearing her say "Oh don't worry about me I am fine.  I am use to it"  It is hard for her to understand that it is not something you should have to be "use to"  kwim?

Anyway we can only be there for her and help her if we can. 

Our son is aware that we are concerned about how this will effect him and promises to keep us in the loop when it comes to his g/f and what is going on in her family.

Some great services and their providers for the Reconnet Program in Victoria. It is the same service as is offered by our local RAFT team. They are fantastic and you can just get some verbal advice from them.

Oops, forgot the link...

http://www.fahcsia.gov.au/our-responsibilities/housing-support/programs-services/homelessness/reconn...

http://www.fahcsia.gov.au/our-responsibilities/housing-support/programs-services/homelessness/reconn...

Horrible for the girl, but I would be visiting/contacting the authorities about the younger sibling. That young boy may well be at much greater risk than the daughter, especially if she moves out and he is on his own in the kind of volatile home environment the OP describes.