This is book number 2 in the Elfhome series.
A New Breed of Adventure
Tinker: just a quick-witted girl from Pittsburgh--who happens to be responsible for depositing high elves and her hometown humans into a melting pot of magic. Now the draconian oni seek to destroy the elves by breeding human git to do their evil bidding. But half-breeds who are half-human may not be the slaves the oni imagined. The revolt is on Its leader--A certain newly-minted elven princess from Pittsburgh, PA, by the name of Tinker. The thrilling sequel to Tinker by Wen Spencer, winner of the 2003 John W. Campbell Award for Best New Writer.