Cat chewing and pulling back claw - not the usual nail biting

I adopted a rescue cat about 6 weeks ago. She's always messed with her left back foot - 1-2 claws in particular. She pulls them until they are raw and bleeding. She will also randomly shake that foot. I took her to the vet and he finds nothing to cause the reaction she's having. He gave me a steroid spray to keep on it but there is no improvement. I found out after I rescued her she tested positive for FELV - which didn't deter me in the adoptions process. But that being said, with her immune system compromised, I do not want to risk infection. Any ideas? She plays regularly, eats like a little piggy, sleeps, purrs, grooms, and loves attention... just can't figure this foot issue out.

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@nanook0811....Bless you for adopting a FELV cat.

Did the Vet do an x-ray on the back foot?

(one of my previous cats had an impacted knuckle, but was limping, and the vet, at the time, said it would go away. It did.)

Does it look like she can get any litter in between her back feet or claws, which might irritate them?

Can you also see if the outer sheath of the claw is intact, and growing over the inner, newer nail?

Sometimes the outer sheath will not come off easily, and causes the claw to curl, so the cat tries to pull it off.

I would ask your Vet if I could soak the foot in some type of warm water, with some sort of antiseptic in it, or something soothing, which may disinfect and moisturize the back nails.