Megapixels and higher are used for those professional shots like modeling poses, headshots, or poster size pictures of people or landscapes.
Don't limit yourself to straight-on headshots.
Instead of the K-11 yearbook photos that are simple headshots on a plain gray or blue background, senior pictures have a variety of poses and backgrounds designed to capture the essence of the subject's personality.
In order to prepare for shopping yourself to agencies, get headshots done by a respectable company.
A portfolio is a collection of headshots, and full body shots that will show off your daughter's talents as a model.