Something else that might work good is having a lunge line behind her butt. This would take two people unless you tie the other side of the lunge line to the trailer. You would hold it behind her butt and when she backed up it would apply pressure and encourage her to go in. Of coarse you would give in take with the rope as she moved forward or backed up. This has been very effective with a lot of horses that I have seen having trouble loading. It seems to have less escape routes. I have also found that holding a lunge whip behind a horse will also get them on the trailer with out even touching them with it. You may need to tap them on the butt a few times with the whip but nothing harmful.