Emily I still don't understand what you mean, could you find a picture on the web and paste the link here? I can't picture her posture.
On the muscle is when they are very tense and not using their muscles correctly when working which isn't good for them
Circles until she calms down and then go straight again once she has slowed down.
Also many short stride trotting poles help, many changes of directions, transitions
What is "on the muscle"?