Thanks jjj111, I've been feeling a lot calmer and clearer-headed these past couple of weeks. Which is exactly why I'm feeling like I can't let her back in right now. I know I'm still really vulnerable and could easily get sucked back down.
If I have to set a boundary, she's either going to get pissed and try to make me out to be evil and uncaring, or she will get completely depressed and make noises about how worthless she is and the world would be better without her in it.
I know exactly what her methods will be and can see through them from my safe distance here tonight, I'm just worried I will let the guilt-trip get to me and cave like I always have.