Vets and pet supply stores have plugin calming liquid. You plug it in near where the cat spends most of its time and it slowly releases a chemical that naturally calms the cat down. This could help with the licking since it stops the cat from feeling like something is wrong. Also, try playing with her more. This can occupy her so that she doesn't lick as much. Cats will lick if they are stressed or feel that something is wrong, especially outside because they can't fix that. If there are other animals outside, be sure to shew them away. Another thing you can try is to check your home. Is there a problem with something? Did you throw out a favorite toy? Is there a new cat or dog? Finally, she may feel she isn't keeping her fur clean enough. Try brushing her daily. This stimulates the skin and keeps her coat shiny, it can also give her the stimulation she usually gets from licking her belly.