Gluten intolerance can present itself in several ways. The following are some example signs that your cat might be reacting badly to grains in her food:
Fur loss (above and beyond the usual kitty shedding, these usually show up as bald spots on her skin);
Excessive scratching;
Redness or inflammation of the skin; and
Skin scabs, tenderness, or soreness.
These are quite general symptoms, however, and could be the result of any number of food intolerances. It's always best to visit your kitty's vet if she starts to display any of the above symptoms — you can have them checked out and diagnosed. Don't worry too much if your cat is gluten-intolerant, as switching to a grain-free diet is often enough to eliminate the symptoms entirely.