Article courtesy New York Magazine, on newsstands now: Meet Mamie Gummer. Her mother is Meryl Streep, but that’s not why you should know her. It’s possible that the first time you behold the luminous, lemon-haired Mamie Gummer will be on Broadway, in the Roundabout’s production of Les Liaisons Dangereuses, where you will watch the dastardly Valmont ravish her, deaf to her convent-girl entreaties. Or maybe you will catch her in the Tribeca Film Festival, where she appears in the romantic short “All Saints Day”, as a mascara-bleared Tinkerbell, making the walk of shame the morning after Halloween. Perhaps you already saw her in Stop Loss, as the young wife of an Iraq-war vet; or in John Adams, on HBO, as the president’s long-suffering daughter-in-law, Sally. But chances are, whether or not you know it, you most likely encountered Gummer long before this prolific April, in the 1986 movie Heartburn, when she appeared as a 2-year-old on the hip of her actual mother, Meryl Streep, and on the lap of Jack Nicholson, who played her dad.