A large number of non-model females are a little flabby (not well toned) now days but they don't want to come off that way in their photos. In this case you've chosen poses and lighting that has not done much to minimize the flabbiness (particularly the arms). #3 is the best shot in this regard and #2 the worst (due to cropping and leaning back against the wall). Also for a "seniors" shot you want better control of hair and makeup.
Re: HS Senior Shoot
Cheers,
rfs