It's so frustrating, I know! Bacca's been doing this on and off routine for months until I finally just went even though he was healthy at the time.
You think to yourself, enough, time to go back to the vet, and then all of a sudden they are better again. So you hold off, and then they get sick again....over and over and over.
Bottom line, don't wait too long to get to the bottom of it, even if means talking to another vet. You'll save yourself and your pup scores of frustration! I don't think what she's going through is something that will disappear on its on. I think you need to get to root cause soon.
Good luck! I feel for this poor little girl. It can't be pleasant for her either!