By Robin McKinley. This is the book that The Hero and the Crown is a prequel to.
This is a pretty exciting book, and, in fact, I was afraid of the horrible things that McKinley might do to her heroine. Maybe I should have known better.
However, it isn't perfect. The events that occur in the ending are past credulity, which is to say, it felt forced rather than natural. Also (I suppose this is more a criticism of The Hero and the Crown, perhaps), some of the elements that were in The Hero and the Crown have mysteriously disappeared from sight. It is probably being too generous to assume that the author had them in mind when she wrote this book rather than adding them when she wrote The Hero and the Crown in order to make a better story.
This book is decent as light, entertaining fantasy, but not as well written as The Hero and the Crown, in my opinion. If you're looking for a more complex plot where the issues aren't quite so clear-cut, you might want to look elsewhere.
There's also a random St. George reference--he's mentioned by name in connection to dragon-slaying! Is Damar really supposed to be part of our world?