Huh, sorry, not much help here, if her teeth have been done, she doesn't have worms and is being fed that grain... It could be something else, such as Ulcers, so I would have the vet check her out. Also, could she be lacking a important mineral or vitamin in her diet? Does she have a stressful enviroment such as no other horses around, or only an hour or two of turnout and such? Also, I would highly recommend free choice grass hay, with supplemented Alfalfa hay, as that can help horses. What are her living conditions like? Pasture 24/7, or night stalling and turnout during the day?
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown