I second HRP's recommendation to try slippery elm bark powder. It was the only thing that helped my IBD kitty many years ago.
http://www.littlebigcat.com/health/slippery-elm/
(Also just want to mention that a cat can still be dehydrated even though they're drinking lots. Not saying that's the situation with Aubrie, but in case anyone else with similar circumstances reads this and thinks they're safe cause their sick cat is drinking - it's not that simple).