Hi Shaw. If you’re working with a 13 year old “unmotivated girl” I guess the first question is who wants the training/exercise? I work with many young clients and I always take the time to speak with them (away from the parent) to find out exactly who wants the training and what it is that they want. I’ve had my share of ‘unmotivated young clients,” and one common theme that I’ve used is exercising within a ‘game” atmosphere. I like Suz’s suggestion of using ‘their music,” and I would add that planning ‘exercise games’ for her might help her embrace exercise or at least enjoy your time together.
I hope that this helps.