having a mother who gives herself a mental breakdown from trying to live to an impossible standard could do real damage.
Your job is not to be the perfect mother. Your job is to be a good-enough mommy for the child you have to get what she needs - not everything she wants. And that starts with taking care of yourself well enough so that you can take care of her without having a breakdown.
HTH
Yes, that exactly. You've received a lot of great advice on this thread. My suggestion would be to pick a couple of things that you can commit to like maybe two or three times a week exercise class and getting out at least once every weekend for two hours without her. Do what recharges your batteries most - coffee with a friend, time alone reading a book, going to a matinee or whatever.
Once you commit to those things circle a date on the calendar - maybe three months for now. If you aren't feeling significantly better I think it is time to talk to a therapist and see if you would benefit from some more formalized help in learning to recognize your negative thinking patterns and find ways to get in a better place.