Does she actually walk away?
Horses, like humans, have a personal space - a bubble, if you like. Some are bigger than others. As you approach a horse, you will hit the edge of the "bubble". The horse, particularly one that doesn't know you well or that is a bit anxious, may either walk away to maintain distance OR may simply turn its head away. If you respect the horse's bubble, stop immediately and take a step back ie acknowledge the "bubble", the chances are that the horse will turn its head back and look at you. A horse that wants you to "come in" will look at you with both eyes and with its ears forward. Approach again - it may turn away again, in which case you have a choice depending on the circumstances - continue to approach (at least you have acknowledged the bubble) or continue to approach and retreat until the horse is comfortable.
Assuming the pony is in a fairly small area, take the headcollar - don't wave it around but don't hide it (never sneak up on your horse - that's what predators do). If she walks away, keep going towards her ie put some pressure on her. Watch her body language VERY carefully especially her eyes and ears because timing is crucial. Keep her moving- don't allow her to graze but don't yeehaa around the padock either or SNEAK, never sneak. Keep your demeanor soft. At some point, she will either stop and look at you or turn an ear towards you. At that point, stop and either take a step back or turn and walk away. She may follow you or she may allow you to approach when you try again.
If she doesn't stand, pressure and release again until she does. She will soon learn that if she does what you want ie stop, you'll release the pressure. Once you can approach her with the headcollar, you might just want to give her a rub with it, then go away. Next time, if she's comfortable, you can put it on.
Personally, I like a thin rope halter - natural horsemanship, if you like - as it doesn't encourage the pony to lean against it. The broad "normal" headcollars are too comfy if the pony leans on it. Again, if you are using a rope halter, timing is important - if you want to teach the pony to walk forward, put on a very light pressure and give her time to respond; if she doesn't, up the pressure but as soon as she gives to the pressure - even a lean forward, not a step - release the pressure - that's her reward for doing as you asked. Then ask again until she has learned the lesson.
NEVER lose your temper - if you are getting cross, stop and walk away. Remember, she's not trying to upset you or be difficult. You are a predator, she could be your dinner - so until she trusts you not to eat her, be sensitive (not soft).
Sorry to go on - you'll find the books invaluable. If you can get to a Richard Maxwell, Kelly Marks, Michael Peace clinic, you will learn loads.
