Flea collars are not very good for cats, It can do more harm than good. It also doesn't do a very good job killing fleas, its more of a preventitive measure. Try Revolution, you can get it from your vet. It is very good!! Your cat will be flea free with in 24hours. It starts working instantly. You may have to treat any carpeting or rugs to prevent reinfestation and to prevent the kittens to be from being infested. But treat the carpets without the cat being around, since the products used are not good for her health. Revolution is safe and the vet will give you a 3 month supply of it. I used it on my flea infested cat and his fleas were dead fast. All I had to do was bath him the next day since he had a lot of dead flea dander, which is because he was really bad with fleas!!!