Cat overgrooming

Hello all.

Years ago, I got a 2nd cat to keep 1st company. Now I have 2 that don't get along; tolerating each other at best, and hissing/avoiding at worst. I've tried the re-separating thing from Jackson Galaxy, but I think it's been too long for them. Both have plenty of space, I give them attention.They're just scared of the other it seems.

Main Issue:
Little one scratches herself to scabbing, grooms herself bald. I’ve ruled out fleas, vet says shes healthy (no bloodwork done was offered during visit), I don't use fragrances/perfumes,

I'm just not sure what to do at this point. Briefly tried prozac, didn't seem to make a difference and it's expensive for me right now. Same with the vet visit, I'm not sure If bloodwork would give answers but I'm willing to try once I get finances in order. I'm also just not sure if she's itchy, its a nervous tic, or if something else is wrong.

Any advice or insights would be greatly appreciated.