It is a dicipline problem. It is ok for a horse to get excited on a hack, It is not ok however for them to misbehave because they are excited.
I expect my horses to hack out in a group and whilst they may get excited I expect them to walk trot and canter sensibly in a group and go back to walk when asked. I expect that the only sign of excitement should be that they are quite forwards.
I expect my horses to go for a good gallop up a hill in a group and to come back to walk sweetly and quietly when told to, WITHOUT a fight.
It is a discipline problem, you need to remind the horse that you are the boss and she puts her feet only where you tell her to and nowhere else.