A Heart's Home, Journey of the Heart Series by Colleen Coble and published by Thomas Nelson.
Isaac Liddle wants for nothing more than to marry Emmie. But what he doesn't know, is that she is hiding a secret from him. Emmie knows she shouldn't hide her pregnancy from him any longer, but before she can tell him her secret, a widower friend asks the impossible of Emmie: will she honor her promise to his dead wife by marrying him to care for the orphaned baby?
As the Sioux Wars threaten outside the fort, Emmie's solemn vow threatens her happiness from within. Will she honor a promise sure to break her heart - and Isaac's? Or is there another way to find a home for her heart?