Who is Isabel from Legends of the Fall and what is their importance?

Isabel is Ludlow's wife in Legends of the Fall. She serves as a steady force in Ludlow's life, although she leaves the ranch each winter to enjoy more civilized companionship and milder winters in Boston. Each winter, however, she also takes lovers. Isabelle plans for Susannah to marry Alfred and tries to keep Samuel out of the war. She disapproves of Susannah plan to marry Tristan.