Lyndsey, welcome to the forum. I hope some members here can try to help your situation. I'm sure your kitty is overcome by stress -- due to the medical condition and the fact that you, yourself, are probably stressed to the max over this. Know that cats prefer to use a litter box. If you have only one, then get another or two more and place them around the house. Some cats prefer open litter boxes, others prefer closed. And cats have a certain cat litter they may prefer. That being said, you're blaming her litter box habits on her medical condition. How did the vet determine there was an air bubble? If every test you did came back normal, did they do a CT scan? Or some type of scan showing the insides of the cat? Personally, I'd see another vet for a second opinion. Irritable bowel syndrome is common in bengals.
Read through this article on how one woman cured her kitty:
http://www.naturalcatcareblog.com/2012/ ... t-by-food/The last thing you want to do is self-diagnose a problem and it might not be that, however, diet can definitely help or hurt a condition. You want your little girl to feel better -- it can't be easy on her. Nobody likes to have diarrhea. I wonder, too, if perhaps she has Tritrichomonas foetus (TF). Most vets do not automatically test for that. It is a parasite that only one drug can cure it. There is obviously a medical condition going on here. I would add a couple of litter boxes and I think once you get the condition under control, the litter box habits will improve.