There are several Clementine/Klementine/Clementina/Klementina Metternichs, but none who can be dated to about 1840 as a young woman.
From Bonhams Web site via pinterest.com/purplerebecca/historical-portraiture/.
This portrait shows accessories for the chic Lady of ca. 1840. The dress has virago sleeves and probably has a scoop neckline.
Keywords: Winterhalter, neo-hurluberlu coiffure, bun, fur boa, lace wrap, scarf, bows, chemise, modesty piece, vee neckline, bodice, scoop neckline, long puffed virago sleeves, cuffs, vee waistline, full skirt, handkerchief