The Managing Miss by Heidi Kimball

She is capable of managing everything . . . except for her heart.
Tasked with making a brilliant match for her cousin, Lavinia Harcourt whisks her entire household, including their two exotic pets, off to London for the Season. With limited funds and few connections, however, the undertaking is not easy. But Lavinia is nothing if not resourceful, and she comes up with a brilliant solution—one that involves her late father’s reminiscences, a forged letter, and an earl.

After years in London Society, Henry Kingston, the Earl of Carlton, has become jaded to those who would use him for his title and wealth. But when Miss Lavinia Harcourt is ushered into his study, bearing a letter that calls in a favor from his late father’s past, he finds himself obligated to help.

Despite his reluctance and her best intentions, Lavinia inadvertently manages to slowly entangle Lord Carlton in her family affairs, charming him with her frank and open manner along the way. By the time she realizes her own feelings for Carlton, however, she fears that the forged letter that initially brought them together may be the very thing that keeps them apart.