Quote:
She goes up the ramp no problem, and stands 3/4 in the trailer.


Good. Now stop there.
Back her out, praise her. Do it again. Walk up, stand as far in as she's comfortable, pause, then back out. Do that about five hundred million times (or as long as the trailer is there).
Don't expect anything out of her the first couple of times. Each time that you lead her up in the trailer, you should be able to get a little further in. Make sure when you back her out that it was your idea and not hers.
Keep extending the amount of time that she stands quietly in the trailer. Then work on her standing quietly without you in there with her. Then work on half-way closing the ramp, etc... All in very slow, progressive steps, giving her some sort of release every time she behaves well.
Each time someone comes to the place with a trailer, ask if you can use it for 5 minutes. Just 5 minutes. In that period of time they'll be busy getting their horses ready anyway.