I agree with Katrina's solution c) and Niomi's solution.
As your horse has never been taught to stand properly, it might be better to find someone with more experience training to help you train her to stand.
Also take into account if maybe your horse only ever learned to crosstie, or stand tie? (Whichever you aren't doing)
Hello Lucy, unfortunately if you do the suggested things below that Katrina said, A) might cause the horse to fall back, panick and lunge forward, B) will only teach her she can break away if she pulls hard enough and C) doesn't seem like a very effective solution, sorry Katrina.
There are several ways to fix this but first you must know the problem is with pressure not directly with tying.
Your horse doesn't understand that when pressure is applied she must go towards it and not away for a release.
She is doing what nature programmes her to do, go against pressure, which in this case is pulling in the halter.
The first thing to do is never tie her with a knot to something until she has learned to come off pressure.
Only wrap the rope around the pole or put it in the ring once.
If she moves around just bring her back to the original position.
If you have a knotted halter so not a flat one you can attach a long lead rope and use a tree.
You send her on the other side of the tree and the rope will too, first at walk and then hold the rope so there is tension once she passes the tree.
The goal is for her to feel the pressure and walk towards the tree, and over the other side and back to you. Once she is very light at walk to it at a slow trot. She will understand that to seek release she has to go towards the pressure so when tied to a wall or both sides she will do the same. It will take some practice.
I suggest also a professional help you.
Hi Lucy, you have several options. A) keep her in grooming stall or wash stall where there is a wall in back of her b) place break away clips on the cross ties or tie the ends with bale twine so that they break off and your halter does not break or finally c) leave lead rope on horse while clipped to cross ties and when she moves hold the lead rope and ask her to stand while firmly pulling down on lead when she moves and say "stand" eventually you can loose the rope and just say stand lol