After re-reading your question, it doesn't sound like she is biting YOU. She is biting the reins/lead rope. It sounds playful, but annoying to you. If you put the rope in my hand and keep your hand up near the mane with very little slack, she cannot access it. After maybe 10 times, she will have forgotten that habit. Maybe. If she continues, break her pattern with something like a 2-step backup every time she bites it until it represents too much work. Good luck!
For your safety, while working with him, have a halter and lead on him. If he gets more aggressive you at least have something you can push or pull on him. He is out of hand and playing with you now, and you are letting him get away with it. Biting is one vice that should be dealt with immediately and harshly. A nip now is a facial reconstruction later!
I have never had to deal with a horse that bites so I don't have any training advice.I'm sorry your horse is biting you.
Normally I don't think hitting in the face is a good thing, but hypothetically if a horse is biting me, if I could time it right, I would smack them in the mouth with the crop. I'm sure there are a lot of people who don't suggest this. But when I was little there was an ornery lesson pony who bit people all the time. The owner did this once nice and hard and he never bit anyone again. He came to the barn with a bad temper.