By her not standing still, she might not see you as dominant so she doesn't listen freely to what you say. Before each and every ride, put her on the lead rope and walk around the paddock on a loose lead. Do lots of halting and a bit of backing up.
When you want to halt, say 'halt' or 'whoa', take one step then stop. She should stop as soon as you ask her. It will be a gradual thing. Make sure she gets a small rub on the head as a reward. Themn start walking again - still loose lead - and say something along the lines of 'walk up'.
When backing up gently place your fingers on her nose and chest and say 'back'. Release when she takes a step back and praise.
Now for the standing: somewhere in between all of this halting, walking and backing up, gently wrap the leap rope around her neck(so it isnt on the ground), tight enoungh so she can feel it under her neck, but loose enough for her to....well breath. Ask her to stand somewhere for 3 seconds. Say 'stand nice' or whatever. When she does, praise her well. Unravel the rope and continue walking.
This doesn't have to be a long walk, just enough for her to understand that you are boss, you are asking her to behave.
Learning to stand still is another gradual thing. Horses can become easily bored just standing there with nothing to do. Gradualy increase the time you ask her to stand still and make sure she gets lots of scratches when behaving. Eventualy you will have a close to perfect pony!
Voice commandes are things to have! Tag what you want her to do with its own little voice command. I use;
Stand: 'stand nice' Walk on: 'walk up' trot: 'hup up' and backing up: 'back'
I find the circles work the best with Pumpkin when i'm riding him an he misbehaves, he doesn't listen and respond as well to them on the ground. But give them ago, you never know.
Sorry for the book
hope it all turns out well for you and your girl! :)