Why does Mary Todd marry Lincoln in Abe Lincoln in Illinois?

Mary's choice to marry Lincoln is carefully thought out; she sees him, of all of the eligible bachelors around, to be the one with the greatest potential. She does not want social prestige or financial comfort and would live in poverty, "so long as there is forever before me the chance for high adventure so long as I can know that I am always going forward, with my husband, along that road that leads to the horizon."