Take her to the vet. It might be something simple but it could also be a sign of disease or malnutriton. Get her checked out and make sure it's nothing serious.
FYI: It's probably not but paw troubles can be a sign of distemper...if your dog has not been vaccinated against it then definately get her to the vet!
Is it bleeding or raw? Or does it look like dry paws? If it just look dry, you should try some "bag balm" They sell it at pet stores and some drug stores (in the lotion dept, its in a green square tin). It works really well to help coat the area with moisture, its also good for minor cuts and dry elbows on dogs. If it looks raw, cut or bleeding I would take her in just in case. You wouldn't want it to get infected.