Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian. I'd like to help with your concerns about Gaby's lack of appetite, abdominal pain, elevated white blood cell count, slightly low protein count and shaking in her rear legs.
I am glad to hear that her pain is being addressed and that she has had quite a bit of tetsing done. It sounds like you've received good news so far in that her organ function looks fine on blood tests, there aren't any large masses seen on her abdominal radiographs and she is brighter and stronger with supportive care in the hospital.
But that leaves us with the frustration of why her white blood cell count is continuing to rise and her appetite still being off.
Unfortunately cancer often doesn't give us many hints with blood testing unless it has invaded an organ enough to cause organ failure. If the cancer is small or infiltrative, meaning it isn't a large mass but rather at the small cellular level invading organs, then we may not see much change with blood tests. We can see inflammation though with infiltrative cancers, and that would explain her continuing to rise white blood cell count.
It is also true though that infections, and the body's response to them, which is often an increase in white blood cells, can lag behind treatment by a few days. That means that the white cell count can continue to rise even as treatment is starting to work and they are feeling better.
Given her age we cannot discount cancer or an infection so I am pleased to hear that she is scheduled for an ultrasound. While radiographs give us the big picture, organ size, shape and placement in the abdomen, ultrasounds allow us to look at organ architecture and see small changes within tissues and allow us to collect samples form those areas for both culture and biopsy. With her history I believe they will be looking for changes in her intestines or abdominal lymph nodes to evaluate her for primary intestinal disease (like protein losing enteropathy, inflammatory bowel disease or infiltrative intestinal cancer) as well as her other organs.
The other thing I would recommend, if it hasn't been done yet is a urinalysis with culture to look for primary developing kidney disease/infection.
Best of luck with your girl, she sounds like she is in great hands and they are following a reasonable course of action and diagostic testing. Please let me know if you have any further questions.