It looks like O. P. Fersen had a flight of fancy with her broad-brimmed hat with huge bow and ribbons over a white dress with pelisse bodice. The bodice fans out from center front with flounces complemented by a scarf or ruff that forms a vee above her off shoulder vee neckline. The closest modern analog I can think of to her hat are the creations worn to Ascot opening day.
Keywords: Sokolov, Olga Fersen, Countess, Stroganov family, Fersen family, Russian, curly coiffure, floral hat, bows, ribbons, off shoulder vee neckline, modesty piece, pelisse bodice, flounces, high puffed sleeves, waist band, natural waistline, necklace, earrings