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

Isabel is an independent woman and Ludlow's wife in Legends of the Fall. Isabel is a steady force in Ludlow's life, although she leaves the ranch each winter to enjoy more civilized companionship and milder winters in Boston. She takes lovers each winter. She plans for Susannah to marry Alfred and tries to keep Samuel out of the war. She disapproves of Susannah marrying Tristan, perhaps knowing of Tristan's restless spirit. She plans Isabel Two's wedding to Tristan and helps Susannah with her new house in Helena.