Enchantress from the Stars (Elana, #1)

Elana, though still a first-year student at the academy of the interstellar Anthopological Service, is elated by the chance to take part in her father's perilous mission to the medieval planet Andrecia, which is being invaded by colonists from a young starfaring Empire. How can they drive the Imperials away without revealing their own alien origin? The key to the plan is a woodcutter's son named Georyn, who believes the menace beyond the forest to be a dragon. To him, Elana is an enchantress who can give him magical powers that will enable him to defeat it. But she soon finds that this role is no mere pretense and that her feeling for Georyn is deeper than she ever expected it could become.

Critical acclaim for Enchantress from the Stars:

A Newbery Honor Book
A Junior Library Guild selection
An ALA Notable pick
Winner of the Phoenix Award
Finalist for the Book Sense Book of the Year Award