They also say we become our parents..
TAF1, it seems you cant leave because you dont want the guilt that would come if something would happen to her if you cut her loose.
So instead, it seems like you want to be there for her, until she gets on her feet, then it would be easier for you to leave her.
I don't think talking to her will help. She will probably mistake your concerns for attacks on her and her character, and she will get defensive.
Just Draw the line. Don't give her an ultimatum, wemen don't respond to well to such. Just draw the line. Make a decision in your head about how far you will go for her, express it to her and stick to it.