Doing lots of upward and downward transitions has helped me when I've been in similar situations. This helps the horses relax and encourages them to take their time, and they ideally start to wait for you to ask for something instead of just running forward.
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"?