Thomas Phillips’ unknown sitter, early 1830s

Unknown woman by Thomas Phillips, RA, probably early 1830s. Private collection UK
A member is seeking the identity of this female portrait sitter by Thomas Phillips RA (1770-1845). She was formerly identified as ‘Lady Blessington’, but this is unverified. The costume has helped to date the painting to the early 1830s.
Medium: oil on canvas
Dimensions: 76.9 by 62.2 cm.; 30 1/4 by 24 1/2 in.
Known provenance:
Lady Blessington (according to a note in the Curtis Gallery archives);
With the Curtis Gallery, Pasadena California, 1951;
Collection of Eric Morse, San Bernadino, California;
Private collection, UK
Suggestions are very welcome; please use the comment facility below.