Get her in the round pen, put the halter and lead on, and leave her. Let her step on it and hit it a few times. She'll get over it. This is how we teach babies to respect a halter too.
After she freaks herself out and does her thing, go back in there and take off the halter and make her move her feet in the round pen. Be sure you distinctly "point" in a direction, and make her move NOW. Not two seconds from now, not a minute from now, but IMMEDIATELY get her at least trotting off, if not loping. Change directions a lot. Step in an "L" shape. Step in front of her shoulder to catch her eye, then take four or so steps back while "pointing" the other direction. This gives her room to turn into you.
Never let her turn into the fence/away from you in the round pen. Every single time make sure she turns to the inside, toward you. Turning her butt to you is a lack of respect. If she turns away from you, run in front of her again, make her change directions and CHASE her for half a lap. Then let her go for a little bit, and ask for the change again. The entire idea behind this is keeping her attention on you, and teaching her the easiest place to be is facing you. If she turns away from you, it will be a lot more work for her.
Another thing to remember when you stop is to step in front of her shoulder, and catch her eye. Let her turn and face you and just let her stand without approaching her. Then go ahead and walk towards her with the halter in your hand. If she holds still, put it on. If she tries to back/run away from you, chase her around the round pen immediately. As soon as she tries to "leave", make her leave hard and fast. She'll learn that moving her feet gives her nothing but trouble and standing still is much better.
Once the halter is on calmly, rub her with it. Throw it at the ground, over her back, around her legs, just general desensitizing. If she moves, follow her. Don't try to stop her. Don't stop moving the rope either. Just follow calmly until she stops moving and relaxes. Make her think the only time she gets to relax is when the halter is on. You could give her a treat too if you wanted but at this stage I wouldn't, since she's being disrespectful with her head.
From there, advanced to yielding her hindquarters and forequarters, sidepassing down the fence, backing up, flexing side to side..All basic groundwork. I guarantee your problems will solve themselves this way.
Pssh.I didn't pick up the wrong lead
It's called a counter canter...
...A very advanced maneuver.