Theodora Hendrix and the Monstrous League of Monsters by Jordan Kopy

The first rule of the Monstrous League of Monsters is: Keep monsters hidden from humans. But when zombie George and his cat companion Bandit find an abandoned baby, they can’t leave her to be eaten by hobgoblins. So they spirit her home where she quickly becomes part of the family. Fast-forward ten years, and young Theodora doesn’t seem too scarred by her monstrous upbringing. But now a series of anonymous letters suggest that someone is about to reveal their secret. If Theodora doesn’t act fast, she may lose her family for ever…