Finish the course of antirobe tablets to get her gum infection under control before using any pro=biotic as they can interfere with each other. See how she is in a couple of days. It's unlikely the antibiotic has upset her stomach, more likely the stress of the vet visit or a reaction to the food she's on.
I personally don't believe there is any benefit in "breed specific" foods, and that it is a ploy from the food companies to charge caring owners more money for the same thing you can get by much cheaper means.
Check the ingredients of your special RC food and if it's high in grain or cereal I'd bet that is the cause of your cat's tummy troubles.