I am working on training one too. It is not going real smoothly. She just doesn't get the driving from behind. She was a riding pony first so she is used to commands from the saddle.
I havn't had this problem before.
Just guessing here, but might try driving her from the side. Like behind the saddle, kind of at the hip, 3/4 of the way back from her head. She might feel like you are not so foreign to her. Also if you have someone lead her for a few times, and I think I suggested putting the longlines lower on the saddle like through the tug loops or through the stirrups of your riding saddle, and trying an open bridle to start.
She will get this!!! It will be like a light bulb switches on, and she will have an "ahh-ha" moment.