Well she is a big girl, and so much weight on those legs could be a problem if she's jumping up by the fence.
Maybe she came down a little hard sometime?
Whenever Ozzy falls off the bed, or something to make him limp, I jusr rub his paw and leg for a good ten minutes. I rub inbetween his toes, on his tones, and rotate his wrist, meaning I softly rotate it in small circles. He squirms a little bit, but after a couple minutes he just sits and enjoys it!

Boy, I hope she gets better.