From Wikipedia; sepia tone removed by gogm.
Lily Elsie is presumably dressed in Pontevedrian folk dress, Pontevedria being a country like Duchy of Grand Fenwick, Sylvania, or Freedonia. Lucile got her big break when she designed costumes for the English language premiere of Lehar's The Merry Widow, played by Lily Elsie. Cecil Beaton wrote an autobiography decades ago where he raved about The Merry Widow. I saw the ballet version and do not recall any costumes as folksy as this one.
Keywords: 1907, Lucy Duff Gordon as designer, Lucy Duff Gordon, Lucile, Lucy Sutherland, Lady Duff Gordon, The Merry Widow, Lily Elsie, theatrical dress