Oh Kitten, I'm so sorry you are having such problems and had an injury :( Just an off question does your trailer have mats on the floor? I'm just curious if it could be the noise that is bothering her if you don't. What color is your trailer? I may be way off here but I have noticed with us it seems dark colored trailers are harder for some horses. I'm just grasping at straws here
If all else fails use the feeding in the trailer. I know you don't like using food, but you may have to as a last ditch effort. The main objective is getting her comfortable in there.