The Blue Sword by Robin McKinley
Mass market paperback format. Highly recommended! An excellent and fierce female-forward tale.
This is the story of Corlath, golden-eyed king of the Free Hilfolk, son of the Lady Aerin.
And this is the story of Harry Crewe, the Homelander orphan girl who became Harimad-sol, King's Rider, and heir to the Blue Sword, Gonturan, that no woman had wielded since the Lady Aerin herself bore it into battle.
And this is the song of the kelar of the Hillfolk, the magic of the blood, the weaver of destinies...