The Unicorn Girl by Anne McCaffrey

Found in a survival pod in space by prospectors, the infant Acorna soon exhibits the ability to analyze deficiencies in plants by taste, purify water and air, and heal. Taken to the planet Kezdet to avoid scientists who want to study her, Acorna discovers barbaric child-labor practices and vows to rescue the children. McCaffrey and Ball have created a magical alien in this fantasy/science fiction story. Recommended for sf collections.