She should not be confused with Harriet Mordaunt. Caroline Mordaunt’s article in thepeerage is here. She was probably married to Gustavus Smith (m. 1853) when this photo was made after having six children with Sir John Mordaunt (d. 1845).
From Paul Frecker, sepia tone removed and enlarged one fifth.
Caroline Mordaunt wears a high crinoline era dress with wide pagoda sleeves and a full crinoline in this photo.