Probably boredom. Get a small hole hay net to keep her occupied.
Also, more turnout…you can never have too much turnout.
Be careful if you use a topical on the wood, I’ve had them actually give horses mouth ulcers, so I don’t use them if I have no other choice…and yes, they were designed for horses.
home to 6 overly spoiled, fat, shiny, adorable horses, and 4 cute barn kitties