In any case, asking the mare to move on out in the posture she held would have set her up to fail. Since there was no story of the mare bucking her rider off, one might guess that piling on the pressure right then is precisely what would produce “planted feet.”
Under the circumstances, “planted feet” in this mare might also be viewed as a generous act of partnership in her decision to keep her back feet on the ground, despite being asked to liven up when her front end was stuck. Either way, two things needed to change for her to be able to move out smoothly with ease: a physical change in posture, and releasing her thought to brace.
Her breathing was less shallow now, and a hint of curiosity had crept into her expression. This is the spot I was hoping to see - a window to her mind and the opportunity to layer in some real change for the better.
I released her up at the wither, to cause a change of posture and shift of her weight up and back onto her hips, then invited her to move forwards, while she was shaped to do so easily. The release at her wither also helped me connect with the instinctive horse in her, and bypass for now the conditioning. She moved up into a nice free trot, with a soft topline, and travelled smoothly on the circle, without a thought to stall out. She hadn’t really had that thought to begin with, I would say, and this response now was just a reflection of her desire to get along, with her body now shaped so that she could.
After that one experience of releasing forward, in a way that did not trigger her conditioning to tighten, she remained available in her transitions, and was responsive to requests for different speeds.
With that sorted out in both directions, I then released her into a turn on-line.