As a teammate, I can tell you she eats a ton (and very healthily), and her thinning out is a result of higher levels of training. You try moving up from 30ish mpw in high school (and injured freshman fall) to running mileage in the 70s with lots of core, push-ups, and drills without getting a leaner body.
She is the real deal, and has consistently improved for two years since she burst onto the scene in outdoor as a freshman. Mega talented and one of the toughest runners I've ever met.