Similar to this?
Jackson was doing this, and it ended up being Lymes. He tested positive with a simple fairly inexpensive blood test and was put on antibiotics and pain meds. Within 6 hours, limping was gone. X-rays were done too to rule out anything else, for my peace of mind, but it was a lot more expensive.
I would start with a Lymes test. You really can't let your dog continue limping, I'd try to get her to a vet.