I don't know about the nosepiece; that may end up making it worse. Maybe if you first try training it out -- as soon as she starts tossing, step down 1 gait (man, I can't remember the right word for this today!) to a trot or a walk or a stop if needed. If she likes speed, this may be all she needs for encouragement to pay attention to you. Head tossing that isn't from pain, to me is an indication of "I wanna do something else" attitude and shouldn't be tolerated.