Have you tried desensitizing her to the clippers? It could be the sound. It could be the vibration. It could be the sensation of being clipped. It could be the clippers pull her hair. It could be lots of things. We have a busted up set of clippers that still makes noise and vibrations that is taped to the end of a stick about five foot long and we do a lot of desensitizing with them while they are turned on. The stick helps keep us out of the range of strikes or kicks if the horse decided to shoot for the clippers. Don't tie, but keep her on a long rope. Make sure the rope is long enough that if she rears, she isn't going to pull the rope out of your hand or pull you into her. Maybe put the chain over her nose or a stiff rope halter on her so that she can't run through you.
Start with the air around her, then move on to touching her. You want to be able to touch her neck, withers, shoulders, up on the poll, maybe the face if you have good stick control and can avoid bashing her accidentally. Don't worry about her throwing a fit. Stay safe. Don't let her bull you over, run away, push you around or anything aggressive or overly dangerous, and work like she is not misbehaving. This issue usually starts off as a fear of clippers but turns into an "I DON'T HAVE TO!" ordeal. Don't get mad at her, as you can't teach if you are mad. Don't baby her, as she won't learn anything. Turn this into a daily routine either as you groom before you work her, or as you groom before you put her up for the night. And might be a good idea to have another person keeping an eye on you.