First thing is to have blood work done, this will give you a clue as to how her internal organs are working, include a full thyroid test. This is the beginning. You can narrow it further by checking for Fanconi by strip testing her yourself for sugar in the urine. If she has the herina fixed, I don't really see that would be a problem, obviously the loss of Bing would of course have some effect on her. It could be a number of things, but as noted above, first you need to see what the blood work might be able to tell you. What is her water consumption? Has it increased? How about her peeing? More then before? Both of which are signs of Fanconi.
You can go to www.basenji.org and read about IPSID (and Fanconi), however that is only really diagnosed with a biopsy as the only reliable way to know.
Also if there are problems with the liver and/or kidneys, this can easily lead to eating problem and weight loss.
Good luck with her and yes, I would get her to the Vet as soon as possible