Yes, take her to the vet - when you were touching her gently and she yelped, that's a definite sign something is up, that something hurts. I know I get cranky when I'm in pain ...

Besides that, what kind of training have you done with her? I'd work on basic obedience training, like she was a new puppy - part of the point of training is increasing the bond and the relationship between you and the dog. She may be thinking she is in charge, and you need to remind her that YOU, in fact, are the big dog here, she doesn't need to run everything.

Anyway, to the vet!