Yes. Keep her on the lead when you are anywhere near horses or, better, don't take her where horses are. There's no reason to upset the horses and cause them stress. You may, in any event, cause them to stampede, with dangerous consequences to other people. And, of course, if one does land a kick on the dog's head you'll have a dead dog.
If she's with you when a rider is passing you'll risk her causing that horse to rear up, throwing the rider. That could give rise to an action.