Sigh, check out this thread Trailer loading tip, unexpected benefit and a question. it shows one way that worked like a charm for him, just slinging the lariat around his butt, we had a few good loads with that one, until last Sundays melt down.
Tried again during the week and simply got on the trailer first with a bucket of treats, and we had this
Other ideas, if you have a pen you can put her in, back the trailer up to it, and then have someone or someones come up behind her with a gate or a fence panel, haven't tried it, because I never have help, but I'm told it will work.
My farrier said he had one like that, he tied a long lead on her, tied one end in the trailer, and just left her standing, in the end she got bored and just load herself.
It's not pretty but get someone behind her with a broom and rub her butt with them.
Just some things that have worked, or people say will work.