Midnight Reynolds and the Spectral Transformer (Midnight Reynolds, Bk. 1)

When twelve year-old misfit Midnight Reynolds takes a job helping out eccentric Miss Appleby in the mansion down the street, she never imagined her work would involve battling ghosts. But as it turns out, Midnight and her new employer have quite a bit in common - they were both born on Halloween and have the power to see spirits of the dead. But when Midnight learns more about the history of her town, she starts to wonder if she's fighting on the right side.