Do you have someone more experienced helping you? Her issue with the bit might have something to do with how the bit is adjusted in her mouth and/or whether it's the right size or not. It may have nothing to do with the bit itself.
Also, training a young horse isn't something that you just want to jump into without help. There will be issues come up that can be very dangerous if you don't know how to handle them instantly...and there will be small issues come up that might turn into very large ones if not corrected early. Lord knows when I was younger, I made my share of mistakes that got me hurt...and even when I made it out okay, the horse generally paid the price for my lack of knowledge.