It may be allergies
to food or fleas, or other allergy
. You don't have to see the flea that affected your cat
since one flea bite can causing itching for at least a month if the cat flea allergy dermatitis; and the flea could be brought in on clothes, etc.
There are some things that you can try at home, but, if they are not effective I encourage you to take her to the vet no matter how far away.
I would switch her food to a hypo-allergenic, grain-free, novel protein, CANNED diet.