First of all, I think you should turn her around so she can see the other horses with their heads out. She is worried about them behind her, so let her face them.
Also, let her move around as much as you can while you are touching her, at first. Don't expect her to both tolerate you touching her, AND stand still. and having someone hold her head will only make her shut down , tremble and maybe lash out. If she can move, I think she will feel that she has an "out". This is what she needs to feel; that even you touching her is only for a second, and thus is tolerable. So, touch her a bit , then remove your hand , then touch and remove. And like Muppet said, don't remove because SHE moved. remove when you want to, not her.
however. the more you can remove BEFORE pony gets to the point where she must act evasively, the better it will go. It's like now you ask your horse to stand once you stop him. he must stand until YOU say go,but the smart rider makes that wait short enough that the horse doesn't get to the fidget point. So, you help the horse be a winner.
So, pet, but get out before horse thinks she has to get out; you get out first.
let her walk around even while touching her and if you can do it safely, give her a bit more line so you aren't pulling her onto yourself.