The Heart Cannot Forget — Mary Burchell

When Antonia agreed to go as secretary-companion to her unknown Aunt Harriet, she did not take very seriously the promise that she would be made the old lady's heiress. She was startled, therefore, when on arrival she found that the estate was a considerable one and that there was a dispossessed nephew in the person of her attractive cousin, Giles, who had quarreled with their aunt over his engagement to Vanessa. Characteristically, Antonia set herself to reconcile aunt and nephew, and in doing so uncovered some very strange fragments of family history.

She found something else too -- her own conviction that Vanessa was not the right girl for Giles.