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. Also posted to the “Early” “Victorian” - 1837 to 1870 Album here.