D.K.
I am starting the same process with my six 1/2 year old daughter. I think 8 is a great time. Someone told me to take one off and have you stand on that side of her as she pedals, then help her if she starts leaning over. That gives her the support on one side, but not completely going without anything. The big thing is to build up trust with you that you will jog along side her on the side without a training wheel and you will not let her fall over. Then that will help her figure out the feeling of balancing, once she has mastered just riding without the one, then take the other off. The main thing is maybe sometimes someone like an aunt, uncle, family friend teaching her as I know with my daughter more of the battle is her losing patience with me personally, hee hee. I would try the taking one off method, you staying on that side with her and jogging along side. Teach her to not lean a certain way but keep her back up straight and focus ahead of her instead of ever looking down...
Good luck, I have to hit this hard within the next month, my goal is to get her out of training wheels by the time we get her 3 1/2 year old brother a bike this summer!!!