Who is Lettice Wood from A Test of Wills and what is their importance?

Lettice Wood is Colonel Harris's ward. Both her parents died when she was very young, and Charles Harris took over her guardianship and brought her to live at Mallows, his estate in Warwickshire. Their familial relationship is never made clear, but the assumption is that they are distant cousins. She is considerably younger than her guardian, and though she is not beautiful, her striking eyes and elegant manner make her hauntingly attractive. Rutledge finds himself being pulled under her unconscious spell, a detail to which Hamish strongly objects.