The reason that she is allowing herself to be mistreated is because she unconsciously thinks she deserves it. If you try, I don't doubt that you could get her, but if you don't treat her like crap she'll just go find someone who will (unless she fixes herself first.) She has self-worth issues or she wouldn't allow herself to be in the situation she's in (we teach people how to treat us). You can't save her, discojoe, no one can except her. There's a song by Vast called "Pretty When You Cry" that soooooo comes to mind atm...

if you knew how much I loved you, you would run away
but when I treat you bad it always makes you want to stay
(why the fuck am I thinking this is a good thing to share with an ENTp?!)

My point is that until she decides to be well (and wellness is a journey, not a location), you're only feeding into the hurtful drama that is her life.

Now... if the issue is the challenge.... which I TOTALLY understand.... then this is a whole different matter and you ought not make a challenge out of someone so broken.