Enlightening Delilah - M. C. Beaton

Amy and Effy Tribble place an advertisement in the Morning Post and hire themselves out as chaperones to prepare difficult young misses for marriage, educating them in their School for Manners. Stunningly beautiful, the dazzling Delilah has had plenty of marriage proposals. But having once been spurned by Sir Charles Digby, the only man she has ever loved, she is now a hardened heartbreaker who toys with all her suitors. And so it is up to the eccentric Tribble sisters to teach her the meaning of true love again.