Re: head shaker ?????????????
A hackamore is a bitless bridle, so it's often used with horses who have a problem of some sort with their mouths.
It puts pressure on the nose, poll, and chin, rather than the mouth like an ordinary bit would, and it's very unlikely to hurt.
And try the nose net as well, as Sonia suggested.
It may be that having a lot of different riders, all doing different things with her, she'sbecome very confused as to what's wanted of her, and it's her way of evading things.
Hope you can sort something out with her.