In an age when the number of influencers seems immeasurable, the idea that there once was a period of time that a select number of people lived up to that title might sound like a reach.
But the exhibition “Influencers: 1920s Fashion and the New Woman” at Lyndhurst Mansion in Tarrytown, N.Y., focuses on three multitalented influencers from the 1920s — Coco Chanel, Irene Castle and Edna St. Vincent Millay — who helped liberate…