A Lady, maybe Mary Bentinck (ca. 1679 - 20 August 1726) gazes out in this Kneller portrait wearing a Lelyesque dress with puffed and slashed sleeves; Mary Bentinck's article in thepeerage.com is here. The Bentincks were a Dutch family that relocated to Great Britain and became prominent as the Earls and Dukes of Portland. Wikipedia has an article about the Bentinck family here.
Left end of upper edge fixed with Photoshop by gogm.