I don't know of a book specifically devoted to maids, but I know of several excellent histories which will provide you a full picture of a maid's life and duties.

To begin with, I recommend What Jane Austen Ate and Charles Dickens Knew by Daniel Pool. This is a glossy, popular-level work that prefers epigrams over thick texts and quotes, and covers a slightly too-long period of history, but it gives you all the practical data you could ever wish for on the running of a household, the duties of the maids and staff, and all the practical considerations of life. I highly recommend it, hokey title aside.

Moving into more academic territory--though still, technically, "popular"--I recommend Inside the Victorian Home, by Judith Flanders. She moves from room to room of a Victorian household and covers maids in detail.

Additionally, though it does not cover maids, I would be remiss if I didn't recommend Henry Mayhew's London Labour and London Poor, an exceptional work which details (in intimate, point by point detail) the lives and professions of every person who worked in the Victorian streets: from rat catchers to prostitutes to all professions in between.