Good for you for taking her in and for looking for solutions, this is usually an allergy/ sensitivity to the food or litter or scents in your household. Write back telling me more, about her diet and what type of litter you use. Have you had her dewormed?
Did you worm her with only the over-the-counter kind of meds? That would be for roundworms, and you should probably get the vet to give you some Drontal for tapeworms. They are more commonly seen in adult kitties than roundworms, which are associated more with kittens. Tapeworms can recur, since they come from prey (from the life cycle of a flea, actually).
I would take kitty to the vet, and have her checked for tapeworms, giardia, and flea-allergy dermatitis. I would NOT use an over-the-counter flea treatment, but one of the safer and more effective ones available through the vet, like Frontline or Revolution. It sounds like she has flea problems (the internal flea meds like Frontline will also help kill fleas that are in kitty's environment), but don't use Advantage because although people buy it because it's OTC, it can be dosed incorrectly and can harm the cat's kidneys.
Also, do some vacuuming and flea powdering around the house -- sprinkle a powder made for pets to wear, nothing harsher, and then vacuum. Cats will pull fleas out of the environment that the family doesn't even know are there, because the cats' bodies are so warm. You want those fleas to be dead. The dot-on-the-top-of-the-head kinds of flea treatments, if given to all the cats, can clear your house of fleas, though it takes a bit of time. Fleas lay a lot of eggs. So vacuuming and washing the blankets and all is a part of flea diligence. The flea treatment from the vet goes on kitty monthly.
Please don't put off taking your cat to the vet, she sounds really miserable.
Great advice from Anniebrook. I would like to add that Fresh Step is Scented (as far as I know!), and can lead to skin reactions. Try changing to either an Unscented or All Natural litter.
Yes awesome thorough advice there Annie and Jade is also right on abt the litter. Keep us updated ace as you follow thru with the advice...<3