A Knight of Tharnin, Book 1 — Robert E. Keller

Kendra's younger sister was swallowed by a mirror--gone in a blink--and now Kendra is blamed for her disappearance. Meanwhile, her small town lies under a shadow of evil that emanates from a cursed forest, and to make matters worse, Kendra can't afford to pay her electric bill. Can she discover her warrior's spirit in time to uncover the bizarre truth? With nothing left except the will to survive, Kendra is determined to fight to her last breath as dark forces close in.