Hi StraightNoChaser!
I agree completely with Buddhist Wife and Sheik, although I have a few things to add.
Firstly, I think that amidst all this chaos you seem to be experiencing, you have one extremely important virtue – you daughter! I think your search for purpose can end here. Haha. I agree with what Buddhist Wife said about purpose being made up. You create your purpose through the small things you do and decisions you make on a daily basis. Many single parents in a simmilar situation to you put lots of pressure on themselves to be “a good mom” and provide for their child(ren) which are very valid concerns. However, if you take a step back and look at your daughter’s life, she has no clue about any of your problems, and I am sure she is thrilled about life and thinks you’re the best mom ever. She is fed, clothed, and happy! 🙂 That is an amazing thing! If that’s all you’ve got right now, just remind yourself everyday that you are already succeeding at the most important job you have – a mother, but remember to see it through her eyes, not yours 😉

I also always find it helpful to concentrate on the little things when the “big things” don’t seem to be lining up. There was a time in my life when everything was going wrong, I had extreme anxiety, depression, was failing school, etc. In those moments of desperation and helplessness, I find it helpful to just force yourslef to go and complete some mundane, easy task. For example, wash the dishes. But focus on doing a really good, throrough job. When you are done, you will genuinely feel more accomplished than you did 15 minutes ago. When you can’t get the big picture straight focus on mastering the little things, because after all, they make up the big picture 🙂