Her name was Katherine Grimston and her article in thepeerage is here. This photo could date to any time after her marriage to 1839 marriage to George William Villiers.
From the Bonhams Web site.
Trying to date this, at least for my knowledge level, is impossible, but she was born in 1810 and looks to be in her forties. The striped wrap, bodice flowers on lace, hair feathers, tiara, and necklace make this an interesting portrait.