Good groundwork is invaluable. Clicker training can be helpful to teach you both boundaries, because is she perceives you as being unfair than perhaps you were being a bit of a bully. Some horses can take being pushed around and others do not.
I second the views for Warrick Schiller and for clicker training.
This woman even uses clicker training with her rescue parrots. https://youtube.com/shorts/_WbQmK86ud8?si=Ic-xzlhxqkFjBOQp