From bhamwiki.com; sepia tone removed and image size doubled by gogm.
The date threw me for a loop. Is this 1914 - or is it 1924? This photo is at the National Portrait Gallery that dates it to 1914. It would have been an early Madame Yevonde photo because that was the year she went into business. Her curly hair and the feather ornament look 1920s to me. Her dress looks strapless and it is a layering of sheer materials.
Keywords: Madame Yevonde, Lady Helen Vincent,, Viscountess D'Abernon, Duncombe family, Vincent family, Viscountess, British, curly coiffure, jeweled feathered headdress, wrap, trapezoidal neckline, bodice, strapless neckline