Here's your chance. Write BM a letter (I'll post separately for SM letters) tell her whatever you'd like.
I know my coming along in SO's life was really hard on you. I'm grateful you've started to move beyond them. Your initial reaction to me was extremely hard as I have never done anything to be treated like that and I really couldn't understand it. I kept trying to figure our what I'd done to you and it took me a long time to figure out it didn't have to do with me. I'm grateful it didn't take you that long to figure it out.
What I can't figure out now is this: You went to great lengths to have your daughter. You clearly love her. I know you have a disease, but why won't you even attempt to get help to save yourself? Your daughter is likely to struggle with the same demons and what she is going to know is her mother didn't even try to fight them. Is that what you really want to teach her? Do you really want her to end up helpless and dependent like you? You are so much stronger than you know- do you really want your mother to do to your daughter what she's done to you? You tell me all the time you don't want to lose your daughter to me- I love her very much but I'm not trying to take her. You are handing her to me and I really don't understand it one bit.
Also, you don't work. Never have, have no other children. Why can't you spend an hour a week at her school volunteering? That really bugs me a lot because i know you'd never be okay with me doing it either and I won't cross that line.
Going forward, I really hope our relationship continues on this friendlier more cooperative path we're on. I'd like to have that coffee we always talk about. Honestly, I think you make really shitty choices some times, and I also find you to be a kind loving person with a quirky sense of humour. I can work with that.
Now, what would you say?