If the walls are gypsum wall board, I'd make sure she was getting enough calcium...maybe give her organic cottage cheese or organic yogurt as a treat a couple times a day or add it to her food.
If she's just found a new hobby, you can try making a tea of cayenne powder and hot water and spray it on the areas where she is chewing. Test, first, for staining, and make sure she is not as crazy for cayenne as I am before you bother with it, though. Of course, she may just switch to licking the walls if she is!
