Hamster lost her skin?

If I were you, I would make sure your hamster is not in any pain, or bleeding. It takes time to heal, so what you want to do is moniter your hamster closely and see if she acts differently, leave her alone in a cage for a few days, and DO NOT touch the wound, their skin is very delicate, and it would be easy for it to tear. Make sure she gets plenty of rest, thats the best thing you can do, and if it does start bleeding contact a vet immidiately! I hope it helps, and make sure the cat isn't in sight of the hamster which may cause it to be afraid and it may have a heart attack.