Sorry, but going in a completely different direction with this. Past doesn't matter to horses. She obviously became untrained while she was with the previous owner. If she's already accustomed to being back at your barn, start working with her on a longe. Send her back and forth in semi-circles, frequent changes of direction. Yield her hind quarters, send her through tight spaces, back her up, anything that makes you move her feet and puts you back as the leader in her eyes. Mares are tough cookies. She will continue to rule the roost until another stronger mare comes along to knock her off her throne. Horses respect leadership. Once you get it back, you'll be off happily trail riding again.