Is my daughter slowly developing a cat allergy?

My 4 year old is randomly breaking out ino itchy hives (not always or upon contact with our 2 cats) and has red, itchy eyes quite a bit. Sometimes, there is sneezing and a bit of a runny nose. None of these things are consistently bad, but none-the-less, they do occur about every 2nd or 3rd day and Benadryl seems to clear it up quickly. Nothing else in her environment has changed...can this still be a cat allergy if she doesn't immediately break out upon contact with them?