My draft mare has always had an issue with accepting the bridle. In her case it's because she's 17.2 hands, and I am a meesly 5'4, so It's quite easy for her to want to refuse the bridle. It's not because she's scared, or in pain. She is simply being defiant, and knows that the bridle means work.
Teach her to give into poll pressure. That is extremely important! It will help for worming, grooming, or even just to calm her down if she ever gets nervous, or excited. To teach her to give in all you need to do is find the hard bump between her ears. That is the poll. Pinch/squeeze the bump. She may resist and raise her head higher, but do NOT give in! Increase the pressure untill she drops it. Even if she just drops it an inch or so. Always reward her by releasing the pressure. It may take a while for her to learn to give into pressure, some horses learn it instantly.
I assume she probably has nothing wrong with her ears. A lot of horses dislike their ears being touched, simply because it's a senstive area. I have a mini who will not let anyone touch his ears at all. If you happen to touch them while haltering him he will thrash his head side to side. I had an Arabian who also had the same issue, and if the bridle or halter sat too close to his ears he would walk around with his head cocked to one side, ha. Had the vet check him, and found nothing wrong. It doesn't hurt to have them checked, but to me it sounds like normal behavior for a horse who doesn't like the ears touched.
KEEP HORSES IN THE STABLE & OFF THE TABLE !!!!! ♥♥♥