HEALTHY dog food for my sensitive dog?

My dog Lucy is a 4 year old Cavalier King Charles Spaniel. When I first adopted her, she was diagnosed with Irritable Bowel Syndrome and after many food switches, we (my vet and I) decided on Science Diet for sensitive stomache. At that point, I was just happy to get her tummy feeling better; I didn't care about ingredients or anything. She was also on Flagyll (spelling?) every day. Eventually, it got to the point where she was weaned off the Flagyll and I attested it to the food. However, the vet says she might have just grown out of the IBS. But recently, I've done some research on Science Diet and I'm really concerned about the ingredients in her food. I want to try something else but I don't even know where to start. Does anyone have any ideas of HEALTHY dog food for my Lucy's upset tummy?