
I had a very similar issue with my puppy, then 13 weeks, wo suddenly seemed to develop intermittent problems with his dry food diet--the same one the breeder had had him on. I weaned him onto another food for a few weeks at 15 weeks, then gradually weaned him back at about 24--and now he is completely fine. It could have been about quantities he was getting, but he got the same every day, so that didn't really explain it for me. The vet saw him during this time and didn't have any answers either since he was wormed, looked absolutely well and was dirinking, playing, etc.
Good luck with her and hope someone comes along who is knowledgeable aboput your breed...