The Hero And The Crown d-2

There is no place in the country of Damar for Aerin, the king's daughter, who is also the daughter of a witchwoman; and so she befriends her father's crippled war-horse, Talat, and teases her cousin Tor into teaching her to handle a sword. But it is Aerin who rediscovers the old recipe for dragonfire-proof kenet, and when the army is called away to the other side of the country, it is she who, alone but for Talat, rides out to confront Maur, the Black Dragon, the last of the Great Dragons, for centuries thought dead.
Mythopoeic Fantasy Award for Adult Literature (nominee) Newbery Medal