Hello. I am posting for my sister. She has a German Shepard that is black. Possibly mixed. She was a rescue. She was timid but loved to play and was pretty happy go lucky for the most part. About a year ago she started going downhill. She was taken to the vet but they didn't know. She has swollen back knees, she's tired and more weak. They used to run every morning and she now has no interest. Any suggestions if what might be wrong?