Remnants of Magic - The Wielder and Her Guardian, #1

The Master Sword Bryan is an elite warrior on the Prince of Shelkite's council. When Shelkite is threatened by Ret, a wizard-king, the Master Sword is ready to fight. His plans are spoiled, however, when he discovers his assignment is as the personal guard to the young half-blood witch sent to their aid-Alexandra. Alexandra is determined to prove herself to the skeptical Master Sword. Though her powers haven't fully manifested, she's ready for anything, as long as she has her faithful mount, Zhan, and her trusty bow.
As the quest deepens, she knows she must press on. For whether she does or not, she's the key-for either good or evil.