How can I deal without being rude?

Maybe you need to be rude. Shock her out of her self pity. Something needs to change and you are the one young enough to do it. She is blind to everything around her and at this point you are doing the same old, same old. You need to shake things up. It means changing yourself, shaking up your life too but if you want her to live, if you don't want her to drag you down, you will have to do it. Sooner or later it will become your life or hers. Don't let it get that far.