My new mare, Daisy, had a 10 hour ride to get to Colorado 3 weeks ago, then the next day had a 1.5 hour ride to my house. I went to load her today, and she wasnt having any of it... but that isn't an option, as she will be my show mare.
So we asked her nicely, let her think about it... then we backed her hard. Walked her to trailer. Stopped her at the trailer. Backed her. Walked her to trailer. Stopped. Repeated several times. Asked her again and she refused, so we backed her hard and lunged her tightly for 5 minutes then took her right back to the trailer and asked again. She still refused so I went to plan B. Broke out the lunge whip and smacked at her heels until she decided the only safe place was in the trailer. She jumped in.
Went to my lesson, worked her butt, and on the way home she hesitated only slightly before hopping in.
So my advice is ask nicely, then keep upping the pressure until they get in... it seems if they figure out that they can refuse they will keep refusing, so you have to ensure that once you decide they are getting in - you can't stop until they get in.
There is no passion to be found playing small - in settling for a life that is less than the one you are capable of living. - Nelson Mandela