I think the idea is cute, however I wonder if it would be just as cute (and easier to do) with a lavender fabric, cut to shape. She would recognize the "idea" and backstory of the pants and "get it." It sounds like the real pants have been worn and washed to within an inch of usefulness. Not sure if I would want to work with that, particularly as a beginner.
Regardless of what you decide, I think it is a sweet idea.