Sorry man that’s the worst situation. You should somehow be able to convey the message that you want to care about her for her, not because she might hurt herself. Make sure she understands that. You still sound kind enough to do this for her, you can’t just leave her (she hasn’t done anything vile, it sounds all like her disease is in control) so you somehow have to be her special friend. Not just a friend, a friend who she can’t wear her mask with. So you have to call her out on her bullshit in a friendly way, make her know that you know what she is doing, but not judging. Make sure she gets that you don’t get affected by what she does but that she has to stop, for her own good. I do t know if this makes sense to you but I have a friend like this and it helps immensely in my healing process. You got this, you sound very (too much for some maybe) emphatic.