So glad you joined our growing family of Yorkie Lovers!!
No, you are not over-reacting. I would definitely have a discussion with her vet. She needs more nutrients than she is getting from chicken and rice. There are several brands of food that are diet specific for dogs with problems with pancreatitis. There are even home-cooked alternatives to prescription diets - but they take a tremendous amount of care to keep all of the proportions in line with her nutritional/health needs.
One quick question about her throwing up the dry kibble suggested by the vet - is Bella a kibble gobbler? If so, it could be that she is eating too fast and that along with her having stomach issues and changing her food could all be contributing factors.