wow thats really harsh of what Ava did to you. when you keep they're head down they can buck easier, and when they're too high they tend to rear. Just try stopping her and backing her up about 4 paces and make her stand there. making her stand there for a moment will let her think of what she did and after a few times, hopefully, she'll realize that your doing this because its wrong. i would suggest a tie down maybe, without the head too low. what i think happend with ava just by the sounds, is that she pulled the wool over ya, she got away with one thing and now she feels that she has domonice. if you get right off her when she is done her things like trying to throw you, she know's that she won and she'll do it every time. i wish Ava was better with you. thats too bad.