Unless you just started eating something new, I'd say it's the kitten. Of course there's only one way to figure it out. Okay, there's two. You can get her scratch tested at an allergist, or you can go on vacation and see if it clears up, or get rid of the cat (but once a cat has been in a house, it takes a couple months for the allergens to clear out; so the vacation would give you an answer more quickly). If it's food, the top culprits are dairy, gluten, soy, corn, eggs, but of course it could be any food at all (food journals can help).