House of Secrets (House of Secrets #1)
V.C. Andrews

But Dr. Davenport has remarried and his new wife has very different ideas about a servant's place. Now Fern and her mother are subject to cruel punishments, harsh conditions, and aren't even allowed to use the front door.
Yet, for all her wrath, the cruel woman cannot break the mysterious bond between Ryder and Fern. And when Ryder invites Fern to join his friends at prom, there's nothing Mrs. Davenport can do to stop them nor can she continue to guard the secret that haunts the women of Wyndemere—but there's nothing she won't try.
After all, reputation is everything.