The woman portrayed in Andrew Wyeth’s “Christina’s World” (1948) has become one of the most iconic figures in American art. Less familiar, perhaps, is the woman who posed for this painting: his wife, Betsy James Wyeth. Dubbed the “chief architect of the Wyeth mystique,” Betsy shaped the Wyeth brand, Andrew’s life, and art for over seven decades in undeniable ways. Though she rarely occupied the spotlight herself, her influence was everywhere: sh…