Sounds very exciting. Can you give a little physical description of both of you (height, weight, etc.)?
Good luck getting a piggyback ride. Maybe it will develop into more. It sounds like she is proud of the progress she has made in transforming herself and more than likely is proud of her strength and her developing muscles. With a little encouragement she more than likely would love to demonstrate her muscles and strength. Sounds like she is already "fishing" for positive feedback. Give her what she is looking for and she may surprise you with her willingness to "show off."