Thats great that shes improving! With HGE, if it is that, it really makes a difference to catch it early so its great that you got her seen so quickly. I think she would be fine on boiled chicken and rice for a few days, I wouldnt worry about adding an supplements as its not going to be a long term diet. I would definitely not let them pressure you into getting the Science Diet/ ID, but I would consider changing her diet. My three were on kibble, Orijen, and they all loved it but Reese would occasionally have an unexplained upset tummy, vomiting and diarrhea, for a day or two. This happened two or three times over the course of at least 6 months to a year, and then he had HGE. He was treated quickly and much better within a week, but it was very scary and hard to see him sick. We didnt know what caused it either, but ended up switching them all onto Stella and Chewys, which is a premade raw. Id been feeding that for awhile and then thought I might switch them back onto Orijen just because it was easier to feed and they liked both anyway. Within a week of being back on that kibble Reese had an upset stomach again. I dont think I will ever put him back on a kibble just to be safe, and I dont know what caused his HGE, but that particular kibble at least seems hard for him to digest. Even if youre feeding her a great food, it might be worth trying something different, and milder, just in case. Stella and Chewys has worked well for us, but Im sure there are lots of foods besides the Hills stuff that you could switch her to that might help.