Is there any way to put the trailer in her turnout area and putting all her food in the trailer so she has to go in it to eat? I've seen a few horses get over their fear just by doing this.
Otherwise, make sure the trailer is as unimposing as possible - take out any dividers you can, open any doors at the other end, make sure there is no way she can slip on the flooring.. you know, the basics.
If you can, load another horse on first, and see if that works.
Having a bum rope (lunge line or the equivalent) go around their hindquarters to push them from behind sometimes works as well.
Some people will have no problem buying a hard loader as long as the price is right.
Personally, I hate hard loaders.. so best of luck to your friend!