My Horse i half lease from a friend is a mare. She has a Giant attitude, like most mares but i've never seen one act like her. She knows how to lunge, but recently she refuses and comes at me when i snap the whip. So far i got her to walk and trot but she will NOT canter no matter what and if she gets fed up with me trying to get her to pick it up she pins her ears and tosses a buck my way. I Dont know why she does it! Does anyone know how to try to change her behavior?