I would finish off the mice fuzzies (though really they are much too small). Try giving her two in one sitting or one every 4 days. Once you're finished with those, go ahead and try and switch her to rats. You can start her on rat fuzzies. She'll be big enough by the time you finish off the mice. I feed my babies 10-15% of their body weight every 4 days and they grow like little weeds. I have one who went from medium mice (she's a mouser and won't eat rats) to large mice in about a week!