There is a very big difference between wanting to trot but still walking and not being able to walk at all without hanging onto a horses mouth though...
It is a training issue, and it sounds like the woman mentioned by the OP isn't interested in training. However, when we started trail riding, putting Mia in the rear was a good way to have a very fussy mare! She would do rollkur on her own...almost trotting in place, with her jaw against her chest...and slack in the reins. She was a pain in the rear emotionally, and a pain in my back physically.
With time, she has improved. She relaxes better in a curb, and I want to buy one with rollers to see if she will play with them. But on a trail, we normally take the lead, get about 100 yards ahead, do a 180, go back to the others, do a 180, and open up a lead again. She is the tallest, is all leg, and believes it is her job to take the point position: "the lead soldier/unit advancing through hostile or unsecured territory", which is how she views every trail everywhere.
She is vastly better than a year ago, and will now sometimes even lollygag in the rear. I used to have a rule with her: she could choose the pace, and I'd choose the direction. Want to go fast? Guess we're heading away from home or the other horses. Ready to walk? Lets go join the others. But we sometimes did 180s until I