@NiiicoleH, Hmmm... I don't know! Maybe she's afraid she will have kittens?!? LOL It could be a sign that she is pregnant, but I haven't attempted breeding yet in my game. Is It only after breeding that she does this? Is she still doing this? Is there an option to calm her down or comfort her? You could try taking her to a pet park or some other venue off your home lot and see if that helps. It might be best to take her to a place that requires a loading screen incase she needs to "reset". Give that a try and please come back and update us!
Best of luck!