Contrary to popular belief the Dog licking it cannot cure or clean her own wound. She needs immediate Veterinarian help to stave off infection. Covering it would mask an infection. Please seek medical help for her. An infection can cause complete removal of the tail and more problems with the heat of Summer.
You should cover it and take your dog to the emergency vet immediately. You will need to find a 24 hour emergency vet in your area to take your dog to. This situation is very serious, take your dog to the vet!