Introduce it slowly to her face, hold it in your hand first and let her smell it as soon as she touches her nose to it give her lots of praise, then slowly start letting it touch her nose then praise and then start moving it up on her face. If she doesn't like it going higher then back down a step praise and so on! :)
Maybe you could try with a positive reinforcement method (like clicker training for example) :)
You take the bridle off and repeat. She will form a positive association.
Also as a goal you could bridle her from your knees. You lower her head and bridle her from there. It's a fun challenge and it will teach her to be calm.
Sorry it posted before I finished...
Making a positive connection.
2. She just needs to learn.
If she is okay with you handling her head. You can offer her the bit (which is the hardest thing to accept) with honey on it. Without even putting it on. You let her lick it. Then you lower her head and pet her with the bridle. If she's okay you go ahead and put the bridle on with the honey on and place it on her teeth and keep it there. She will taste the honey and be curious. When she opens her mouth you gently push it in and let her taste the honey.
Ok so it could be caused by two things.
1. She is "head shy".
So she will first need to feel safe with you handling her head. Stroking her and touching her everywhere helps. Also stroking her while holding a rug and then the bridle so the bridle is stroking her. Making a positive con
Good thing to do is give a treat after bridling to make it a positive thing, or you could put something sweet like sugar or something on the bit just to make it a positive experience.