Just let her approach and retreat from the trailer as many times as she needs. You can even leave the trailer in her pasture or paddock and leave food inside and let her investigate it on her own terms.
I'm 11 and I had worked with a 17.4 hand horse that is scared of the trailer. I just let him look at EVERYTHING. I let him walk in and back up sniff the bar. I let him look in to the tack room. Then the next day he was just fine. So do what I did BEFORE the show. Or before you leave
I had an abuse case who feared the trailer, I left grain hay and apples and carrot trail in the walk in area and let him find out on his own that entering the trailer wasn't all about force and fear. Trailer was in the free roam area like a round pen plently of room to sniff it all out and get comfortable with everything. Don't expect this to happen in 10 mins took a few hours...
Practice practice practice. Reward any try at all. If she steps up with one foot reward her and make her back off. Do not let her do it on her own otherwise she will think that it's ok to do it on her own. Everytime try to ask for a little more. And everytime back her off. Grain is also a very good way to get her in. If she's loaded in the trailer multiple time and know how then sometimes grain works. Also if she pulls back then don't try and keep her in but make the wrong thing hard. Put steady pressure on her until she finds her release by stepping forward. You can also ride her really good and lunge her before you load her.