I am sorry your poor girl is going through this. It sounds a lot like Fletcher when I first got him. My vet guessed IBD, we didn't do the scope, just started treating as if that was it, and things got better. He was on Flagyl until he stabilized. I never found a kibble he could eat. He can't tolerate most veggies. I started feeding him raw, and he has been doing well for the last four years. He has a few "episodes", usually when I'm not careful and he eats something he shouldn't, but he's never been as bad as he was in the beginning.
You already know she can tolerate chicken. How about trying other meats (cooked or raw)? I would stay away from veggies and grains, except rice since you know she is ok with that. The only veggie exception Fletcher gets is a spoonful of cooked pumpkin (or is that a fruit? ). He eats chicken, turkey, pork, beef, lamb, sardines, duck, no veggies, no grains. (he also gets yogurt) It may not sound balanced, but he's very healthy Maybe you've tried some or all of this, but if not, it might help.