“Ada Louise did not want a memorial service,” Robert N. Shapiro, her lawyer and co-executor, told more than 200 listeners as he opened the gathering in the Grace Rainey Rogers Auditorium at the Met. “So we’re not having one.” Instead, he said, the event was simply a “memorial tribute,” composed of a “coalition of the disobedient” — friends, subjects, colleagues and readers — who couldn’t imagine not saying farewell.