Check her bedding, if you find grains of "rice" she probably has tapeworms. Cheez-it got some a while back and I saw the little white worm segments (about 1/4-1/2" long) in his poop. I checked his bedding and sure enough, rice!! They can get it from eating a flea and just because your dog is on flea prevention, that usually wont stop one from climbing aboard. Mabye later when the pup feels it moving she ingests it while chewing at the itch. The remedy was Drontal from the vet, it was a little pill that he refused to eat. (Some tuna the vet had worked) and 2 days later Cheez-it was fine. She said that it is pretty common for a dog to get it once or twice in a non-flea prone area. I have the receipt and I was charged 10$ and some change for the treatment, so it was highly affordable. Just google for pictures of the rice if you want to verify.