You said this yesterday:
What does the vet mean by "treat conservatively"? The two possible conditions have different treatments.
One test you could do is try to give her different proteins that she has eaten before. For example, if she had eaten chicken before then try something new like lamb, rabbit, or pork. If you also give a good probiotic and a fiber/probiotic like psyllium husk fiber, that may help. If she does get better on a novel protein diet, then it is IBD you are dealing with.