It sounds like she responds to you pretty well...she lets you pet her and seems to like your attention. Do you think you would be able to coax her into a cat carrier for a visit to the vets office. She is probably due for a good checkup anyway and they would be able to help clean her up and see if she is healthy.
I'm sure she would appreciate the care and reward you lots of head bumpies. If she isn't spayed yet and you can afford the cost it would be a great thing if you could get her fixed.
Good luck with her...and kudos to you for helping tend to her needs.