A lot of horses dislike being touched/petted on the front of their face, especially if that is the first place that you touch. I would try putting your hand under her chin and giving her a gentle scratch under her jaw. After a while, keeping your hand under the jaw, gently rub her cheek with the thumb of that hand. Then you can change hands under her jaw and rub the other cheek with the other thumb. Or maybe try cupping her lower lip/chin gently with both hands, maybe stroking either side of her muzzle with your thumbs if she will let you. If she jerks her head away at any time, then simply walk away and try again later. Horses love attention and most prefer you to stay around and pet them than have you walk away and ignore them!
There is no need for you to pat/pet the front of her face for now, just pet her elsewhere and work round to it slowly. Remember they always tell you to first touch a dog by going under its jaw with your hand, never on the top of its head. I always approach my horses with my hand under their chins.
Hope this helps in a small way - good luck and take your time with her, I'm sure she will come round in the end.
Anna