go back to basics-start out with someone walking at the head. Put a halter on under the bridle, and your assistant can lead her forward when you say walk on ( or whatever you say for walk- what the pony knows) . Go through your basic commands of walk on and stand or halt. And as the pony starts to go correctly the assistant at his head can move back to walk near the side at the withers. A couple of sesssions of this, and you can leave the lead rope off, and you can just have someone to go to the head when necassary, but walk back near you when not. The best thing is not to let it be a battle, and just kindly and calmly let the pony know what you are asking of it. The second person can help you in this. You can't expect to stand behind the pony and have it know what you want, unless you start with someone at the head to show the pony that's what you want it to do!