I have the same horse. She was sold at auction so I know had quite a life before I bought her. She will not go on the trailer if she does not want to. Once she is on, she is perfect. I have found I can’t have anyone around who even thinks in a forceful way. Everything has to be quiet and calm. One person on the trailer with the lead line, one person at each side behind her, lightly tapping the ground but never touching her. No one talks, the person holding the lead line has gentle pressure until she takes a step and then quickly releases it. Nothing else and if it takes two hours, then it takes two hours. It doesn’t – the last time she marched right on. We also discovered that she is very sensitive to the bright light outside and the darkness of the trailer inside. So one time backed it to the barn so the light was even between the barn and the trailer. She almost ran on that time. Never use the rope behind her and never try the lead line through the door. Never use anything that has any force and only think happy thoughts the whole time. You horse sounds as sensitive as mine. I don’t have my own trailer so have always had to rely on others to move her – which adds to the stress. I am sure she feels my stress with the whole time. I hope you figure it out! I read all of the replies hoping to find something else that would help. I have tried all of the recommendations listed. What works on most horses doesn’t work on mine. She is unique – but also with that uniqueness is a soft, sweet mare who is amazing to train and ride. She just needs someone kind and she is beautiful. Sounds like you might have the same kind of horse. Almost feels what people think. It isn’t fear or stubborness, it is wanting you to figure out what they need. They try to talk to us in their own little way.