Originally Posted by
thetroubledone 
That's pretty hard hitting. The problem I'd have if I did decide to leave is that it would feel like I would be giving up on her that and the results of the break up could make her situation even worse.
Giving up and letting go are not the same thing. Giving up implies that you have ever had any measure of control over her condition. That is an illusion. Letting go is accepting that she is an individual and an adult, and affording her the dignity of experiencing the consequences of her own choices, as opposed to treating her as a helpless child with no power over her own future.
If you were to let go and her situation were to get worse, it would be because she
chose to allow that to be the result. She would only be using you as an excuse to continue to ignore her own problems. You would not, in and of yourself, be the problem.