What flea medicine did you use? See if your vet will sell you Frontline or Revolution for all the cats and the dog. Over-the-counter products just don't do as much and some aren't even safe. Once all the animals have one of the two I mentioned, the fleas will start to die out of the environment. Also, vacuum everything including the furniture, wash all the bedding (animal and human), and even consider bombing the house. While this is going on, you might consider boarding the cat at the vet's for a while to let her heal up.