"Dragon Reserve, Home Eight"
is a short story by Diana Wynne Jones
A satisfying story which verges on the eerie and scary. A young girl faces execution for something she cannot help, which turns out to be the very thing needed to help save her world from the evil slavers.
It is in several short story collections: Warlock At The Wheel: And Other Stories , Everard's Ride, Unexpected Magic and Minor Arcana.