It's a stress thing.
Both cats have a treatable condition called Flea Allergy Dermatitis, they're allergic to flea saliva. Been battling this for a long while, my mom's cat has it worse, since she's more sensitive then mine. Living in a sandy area doesn't help the situation.
Flea baths + Itch Soothing Baths + Flea drops.
We spray the furniture, & carpets with flea killer too, but it does very little. Summer is horrible when it comes to fleas.
Since it's cold out now, fleas aren't really much of a problem right now.
If she still does it it might be something else like a food allergy or something