Benadryl can be given to cats, but it's for allergies, I don't know that it would work on a wound that was itching as it healed.

Good luck with Precious, Gary. I hope the vet can fit another collar on her, or you can. Figuring out those e-collars is not easy at first. I put them on back to front, with the loops on the wrong side, and all kinds of ways before I figured it out.