How about reading the story of this guy? http://www.our-happy-cat.com/cat-flea-collars.html
"The Poison Necklace A Pesticide collar is nothing but a poison necklace around your pet’s head. It emits a constant toxic cloud that your pet inhales, and so do you, every time you hug your pet. What about those insecticidal flea and tick shampoos and powders, sprays and dips? Labels warn you not to get any on your skin, use rubber gloves and wash your hands! Yet, they are rubbed into your pet’s skin and then are licked by your pet! Signs of pesticide overdose in your pet can include vomiting, diarrhea, trembling, seizures and respiratory problems. Flea Collars: The Cancer Prevention Coalition (CPC), which informs the public about preventable exposures to carcinogens, list many brand-name products as containing either carcinogens or neurotoxins, or both. Avoid flea collars by Longlife, Hartz, Pet Agree, Sergeant’s and Zodiac. Flea and tick dips, sprays, powders, foggers and bombs: click the headline and scroll down the new page to learn more about how to control fleas without resorting to chemicals
That's quoted from this site: http://www.shirleys-wellness-cafe.com/avictim.htm
And there's many other cases out there of cats getting seriously ill from flea collars. It is NOT the least of her concerns. Oh, not to mention flea collars don't actually work, so.... All they do is poison the cat, because the chemicals from the collar are being absorbed through her skin. Skin is a huge sponge, so when you expose it to chemicals in the air, or against the skin, the skin will absorb it, and reak havoc on the creature from the inside.
Now, you can add Garlic Powder to her diet, as fleas don't like the taste of a cat eating garlic. 1/16 tsp Garlic Powder sprinkled dry in her food every day for a week, and it should start to repel the fleas. And of course you have to get rid of the fleas in the carpet. I've read sprinkling salt and baking powder into the carpet, and letting it sit for a day, and then vacuuming it kills them.
Garlic Powder will not only deter fleas, but kill any parasitic worms she may have. There is no risk of Heinz anemia as long as you only use 1/16 tsp Garlic Powder, and only for a week, then wait a few weeks, and if she appears to be bothered by parasitic worms again, use the Garlic Powder for another week. I've used Garlic Powder to deworm 3 cats, and it works amazing. As long as it doesn't get wet, cats'll eat it no problem. And as long as the Garlic Powder doesn't heavily coat the food to the point the smell of the Garlic outdoes the smell of the food, they'll eat it no problem. I recommend using Organic Garlic Powder because...it's organic.
Also, the type of food she's eating will severely effect rebounds of parasites. If cats are fed on raw food, or a diet as close to it as possible, with minimally-heated meat as possible, they will be worm-free after being wormed once. However, feeding the commercial pet food that's infiltrated with grains, and carbohydrates, those actually create the perfect internal environment for parasites like worms, and it is incredibly hard to say goodbye for them forever. People, so long as they're feeding those carb and sugar-laced commercial pet foods, experience a constant struggle with having to deworm their pets. Cats are being fed way too much carbohydrates in commercial pet foods - they don't derive energy from storing carbohydrates, they derive energy from pure meat protein.