Squaw has always been pretty girthy and when you tighten the girth she almost always attempts nipping and she just plain out fusses.
WHen you cinch up, make sure you are doing it slowly, not jerking the cinch. When you first do it, slowly pull back. Then work her to get her breath flowing again, slowly do it again. Then again do it one or two more times. You don't have to be cutting off the circulation of the horse either. (Super tight)
I've tried using my fist and hitting her in the muzzle, but that's starting to make her headshy. Again.
DO NOT do that. Without a doubt it will make ANY horse headshy.
When you cinch up, make sure to 1.) keep your elbow up so when her head comes around SHE hits your elbow.
2.) tie her head up shorter. My horse likes to act like he is going to bite me - so I tie him up shorter and when he turns head to head to go around, he can't.
3.) be quick with this tip: as soon as he turns his head get your hand so your hand makes a king of this shape: > where the top is all your fingers and the bottom is your thumb. That is your "mouth." As soon as her head moves around, quickly move your hand to her muzzle with your "mouth" biting back - but do not pinch her.
4.) get a crop. Tuck it under your elbow and have one of the ends be in the way of where she would try to bite you. So when she comes around to bite you, a crop is in her way and SHE hits HERSELF with it or she ends up biting the stick.
Horses are prey animals - they do not understand punishment. They do however, understand predator.