This is an early Victorian take on panniers with what could be called 30s Hollywood accuracy. Panniers reached to the sides but were flat, this dress is round and probably round due to supports. The cage crinoline is still ten years off, but dresses supported by crinoline composite petticoats are the fashion in 1845. This dress has polonaise-like poufs on the sides. The dress has revers and a stomacher, wavy skirt panels, and strips of ruched fabric for decoration. The skirt is maxi- rather than floor-length.
From eBay; background made uniform white with Photoshop by gogm.
The Lady is probably Elizabeth Catherine Gubbins who survived her first husband, William Aubrey de Vere Beauclerk, 9th Duke of St. Albans by decades and later married Lucius Bentinck Cary, 10th Viscount Falkland.