Made my kitten constipated

My British shorthair kitten had blood in her stools and a lot of wind. The vet prescribed this food. It worked for a few days, but then she became very constipated. The vet told me that I should switch her onto another food as in the long term this food does not provide enough protein. I am now on the hunt for another miracle food that will give me a kitten with a healthy and 'normal' digestive system.