First congratulations on 13 years with a Shepard!! Most live to about 9. That being said, she is old! This behavior is common, She might be in distress, in pain, or having anxiety over something. If she continues to eat and drink that is a good sign. I know that walking her short distances if she is able or just get her outside it might relive some of this anxiety. If you are really worried then take her to the vet. Good Luck!