All I can find out about Marie Georgine Armandine de Sérent is that she married Louis François de Rohan-Chabot, Duc de Rohan, and that she wore this train. This may not be on view.
Enlarged one half by gogm.
The train is apparently attached to a typical or notional Empire dress by a waist band.
Keywords: 1809, Armandine Marie Georgine de Serent, de Serent family, Rohan-Chabot family, square décolletage, neckline ruff, quarter length puffed sleeves, waist band, Empire waistline, close skirt, train, gloves