LNT I am going to ask a stupid question. Are you the problem here? Have you had issues in the past at the beach? Is she so sensitive to your aides that you are stopping her at the beach? I have found with a few people that I teach that when the horse moves forward their hands come up for a split second and htat is enough for some horses to halt. Try anchoring your hands to the saddle as you go forward just to make sure you are not putting on the brakes.