I had the exact same problem when I was training my two year old! I became to forceful one day and took things to fast and it just went down hill from there. Finally, I just too a big breath and the next day, I started over. I made the bit enjoyable for her - slathering it with peanut butter and oats. I let her lick it clean quite a few times everyday. Finally, I would slip it in her mouth and let her spit it out right away. I would congratulate her. I kept doing that and then I would finally put it in for about three minutes and take it out again. She learnt that it wouldn't hurt her and she soon adjusted quickly. Another thing about my horse is that she's really mouthy and loves to chew! I would attach the bit onto her halter rings with clip on reigns and to sit at the side of her mouth. She assumed it was something to play with and she would but it, chew on it, and put it in her mouth herself. Then she could spit it it whenever she wanted and when she walked it would sway beside her mouth and she would become attracted to it. This helped me a lot and I hope it helped you!