We Don't Know Why — Nancy Springer

To a future girl, Mishell, who flies with the aid of anti-gravity wings, the death in a freak accident of a beloved older brother, Mykel, is hard to accept. Why had it happened? To Mykel, of all people? Why ?

Rebelliously going AWOL from her home spacecraft, cruising the sky of an earth-like planet, Mishell is worshipped by primitive people who believe she is an angel. After she rescues one of them, their faith in her is boundless, and she begins to understand the weight of the question, “Why?"

A short story.