My main question is also – is this a new behavior? If it is new and out of character you may want to have her checked for lyme disease. There are so many strange displays with lyme. This happened with my mare. Out of the blue she started backing and yanking off the crossties. Turned out she did have lyme and once treated the behavior stopped. I had a prior horse that all of a sudden started dancing around when he was being tacked up. For him it turned out to be lyme also. Once treated behavior went away. You know what is normal for your horse – so again, if this is totally abnormal for your horse think about having her checked for lyme.