I was in a similar position to you years ago

My (now) ex-wife wasn't as far off the deep end as yours currently is, but it wasn't great. Hopefully she gets help, she clearly needs it.

Just one thing: take care of yourself. You need to be in counseling, too. If you're not healthy, you're not going to be able to effectively parent as well as you're capable. There are times when you're going to feel like there's no way to climb out, and that's when the process of changing your thinking with professional help pays off. Trust me, I have been there, brother.

I'll be thinking about you. Stay strong and take care of that little girl.