Having difficulties standing completely still?

More time standing still will help enormously. When you get your halt, stand still for at least 2 or 3 minutes every time. She is not understanding that you want to stop because you don't stay stopped long enough, she can't see the point of stopping if you are going to ask her to move again straight away. I had this happen with my horse, and let it get so bad before I realised what the problem was that I ended up staying stopped for ten minutes at a time to make her understand. She stops and stands beautifully now, but it was a lot of patience and work on my part