When I teach one I usually start with "walking the square" as I call it. You start with 1/4 or 90 * turns. You ask for a 90 and then stop walk forward a step, ask for a 90, etc. until you have gone all the way back around. Once the horse plants the right pivot foot (that is technically the correct pivot foot for showmanship) you then add the 180 and 180 until it is nice a flowing and she plants her right foot. Then build up to the 360. It is time, patients and repetition. I usually don't "correct" one while they are still learning.....once they know what they are suppose to do that is different. If they step out, continue to ask until they do it correct and then stop and reward them. To help them learn you can put the lead in your left hand, and use your right hand either on the shoulder or right where the shoulder and neck meet. You use the lead to help hold pressure to keep them straight and from walking out. Now, sometimes to help one stay on the correct foot as they are learning you have to watch their feet and weight shift. If you notice they are getting to out in front and look like they will walk out with the back foot then hold them back a little to get back under themselves, if the other foot is in the way help with your lead hand to guide their weight and body so that as they turn you have to help make sure they don't get to far in front, behind or get their feet in the way. That is part of teaching them, is really helping them guide through as they first learn. Go slow and think one step at a time, the front leg should cross over the other front leg, not behind when they do it correctly. Just try and help watch her body weight and her shift so you can help get her balance and foot position back before she steps out.....a lot of knowing and reading your horse....but it always comes together with hard work....Good Luck, I love showmanship so good for you in adding it to your class resume.