Excessive licking can start out as a dog's effort to comfort itself, but the behavior can turn into a bad habit that irritates the skin. Is it a sign of a physical problem, or is a dog reacting to recent stress?
Compulsive Licking Behavior
Some dogs will begin to lick a part of their body excessively. The most common is a leg or foot. Whenever excessive licking starts, you should always first have your dog checked by a vet. If a vet rules out a physical problem, a comment treatment is a low dose of Benadryl. This can sometimes cause a dog to relax and break the licking cycle or if the licking is due to itching/allergy, it can also help.
If the licking started after any kind of stress, for example the death of another pet, the loss of a member of the family, moving, or even temporary separation from the family, stress might be the reason.
Stress Licking Solutions
Dogs can certainly feel their own stress. However, they also pick up on their human's stress too and carry it with their own.
With any sort of stress behavior, the action becomes a soothing habit. You can't correct the habit without breaking the behavior for a significant amount of time, and that would probably require the use of an Elizabethan collar around her neck to prevent the dog from licking.
Another option is to distract your dog each time she starts to lick, either by giving her a treat without acknowledging the licking or engaging her in a couple minutes of play time. Replace the unwanted activity with more desirable ones, but make sure she's not connecting the licking with a reward.
This will not be an easy problem to correct, but you should be able to work away from the licking if you are persistent.