I have no experience with driving but I have had horses that were badly barnsour...one thing you can try is working her in circles (both directions) right next to the barn, as close as possible to the thing she is most attatched to and wants to go back to (her mom, the barn door, her pen, etc). Do it that way for at least 20-30 minutes before you go on the trails, long enough that she gets sick of it. That way, she will likely be happy to get away from the barn, which she has started associating with long, boring work instead of food and security. She will be happy to get out of there! Just one thing I have tried with a previous mare who would dramatically refuse to canter anywhere except but back to the barn...she got over it quickly when we did that for starting at about 30 minutes before every ride, gradually decreasing until she was totally cured. Hope this helps.
He knows when you're happy; He knows when you're comfortable; He knows when you're confident; And he always knows when you have carrots.