By His Grace and Favor by Christina Dudley

She would do anything to save her family, if she could only ignore her heart.
Oxfordshire, 1800. When a series of disasters strikes the Barstows, oldest daughter Adela devises a secret plan for their salvation: she will marry their elderly benefactor, Lord Dere of Perryfield. But her pursuit encounters obstacles, first in the form of the handsome household tutor, who openly disdains her efforts, and then from her own unpredictable, unruly affections.
Tutor Gerard Weatherill faces struggles of his own. Determined to shoulder his way into respectable society, he cannot let anyone draw too close, lest his own secrets be discovered. And clearly the person he must avoid above all others is the observant Miss Barstow. Observant, mischievous, marvelous Miss Barstow. But if he keeps her at arm’s length, will he lose something worth far more than his sterling reputation?