Locked in Time — Lois Duncan

Nore Roberts didn't ask for a new life, but now that her mom is gone and her dad is newly married, she has to settle in at Shadow Grove, the old Civil War mansion her stepfamily calls home. When she meets her stepmother, Lisette, Nore is shocked by her youth and beauty that gives her chills- and a hint of something sinister. There's hope of becoming friends with her stepbrother and sister, until Nore realizes they're hiding something. When she begins to feel like the target of a deadly plan, Nore starts digging into her stepfamily's past. The skeletons in their closet are more real than she ever imagined. Can Nore expose her stepmother's dark secret before an old and evil magic swallows her up?