I would lead her calmly and confidently on a few handwalks down your trails to start. No pressure - just walk her a few days in a row. Make it fun and relaxed. When you get to the furthest point on the trail, before heading back or the middle point if it’s a circle or loop, let her rest, relax, graze - bring a few carrots.
Then, let the training begin. As the owner of a very, very barn sour horse at one time, I can only share what worked for us. Keep in mind I was a scared beginner at the time and 75% of the problem was in MY head. I was nervous, and horse picked up on it BIG time. Set yourself up for success. Put on a western saddle or grab strap if you have to. Before you leave, get your head in the game, as in “Today, we are confidently going to ride on the trail. Period. End of story.” You must get there. My trainer at the time told me to think that my son was in the woods, with my car keys. I had no way to get to him except to ride. He was 5 at the time.
Sit tall, and ride her to the trails. At the first balk, squeeze, kiss and crop. If and when she moves forward, release the reins immediately - reward her, sit tall and walk on. If she does move backwards, put her to work immediately then and there. Trot small circles, yield her HQ in circles and make it enough that it is work for her. Ask her for forward again. If she does it nicely, she gets a loose rein and gets to just walk. That is her reward. The old “make the wrong thing difficult, and the right thing easy…”.
I will say that what made the change and the turning point for us was to dedicate 5-6 days in a ROW to work on it. I found that if I tried one day…skipped a few days, and tried again, we were back to square one. It is best to work consecutive days.
I also became keen to his “set up”. As we walked down the path, he would first start edging right, so he could make a wide turn to the left or spin left to turn back. I started to get ahead of this tactic, keeping my right leg on and forward aids sharp so he stayed in the middle of the path. His way out is still ALWAYS to the left if he tries anything.
My horse was once a nightmare with this. He would do mini-rears, and literally pirrouhette me up the fenceline path back toward the barn doing little spins. It wasn’t until I made my mind up that enough was enough - we were GOING and going now…I sat tall, followed my aids with my crop and meant it, and made sure to release and reward at the right times. Fast forward to today, this horse will ride anywhere alone - trailer anywhere alone and we hack alone all the time. He goes happily and actually prefers to lead now. (He used to only follow, with his head practically resting on the horse’s butt in front of him!!) I would have never, ever believed back then that we would be riding alone all the time today. He is a joy now and lovely to ride alone. So it can be done. Just set your mind to it, train several days in a row and make sure you reward her when she does what is asked. A pat and “good girl” goes a long way.