When you bridle the horse do you push her ears back or forward? That can make a big difference. The ears should always be pushed forward and use the palm of your hand not your fingers to do this. When you unbridle be sure to lift the bridle so it doesn't jam against the base of his ear when pulling it forward. Release one ear then do the other side. When clear of the ears, hold the bridle steady and wait until the horse releases the bit. If you just pull it off the bit hits it's teeth. That will cause this reaction.