Some information about her can be found here. Her husband may have been a prominent banker who bagged himself a title. Kind of like Steven Mnuchin, the US Secretary of the Treasury, especially if baron Mallet came from a family of means as did Secretary Mnuchin.
From en.gallerix.ru/storeroom/1941543836/N/8009/; removed print in area surrounding oval with Photoshop.
Baroness Helene wears an unusual hair ornament and a bertha made with a ruched strip and lace complemented by lace engageantes.
Keywords: 1851, Winterhalter, Bartholdy family, Mallet family, Helene Bartholdy, baronne Helene Mallet, baronne de Chalmassy, Baroness, French, straight coiffure, braided bun, hair jewelry, fitted bodice, off shoulder neckline, ruching, lace bertha, quarter length sleeves, lace engageantes, full skirt, wrap