Could my ferret have allergies?

My ferret roxy is white with black eyes recentley shes been super itchy but today i noticed some of her fur is turning red i gave her a very gentle bath wih ferret shampoo to clean her up and i noticed she has like an orange dandruff under the fur that is turning red and inbetween her toes behind her ear and on her belly where the scar from getting fixed is.I know this means allergies in dogs. I recentley changed her food from the marshalls diet to evo grain free diet. the only thing is that my other ferret disco is doing all the same stuff eating the same food sleeping with roxy and everything and she is perfect so what gives ?