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.