probably due to salt put down when snow was around. Val will have some witchy woo woo remedy for this.
would wash in diluted hibiscrub & put some sudacrem on it or thovaline (stuff used on baby's botts for nappy rash) Keep herm from licking it - do it when you know you will be sitting with her for an hour or so.
Go to horse/country store and get some paw wax for future.