Mary, Lady Barrington Bourchier (d.1700) attributed to Willem Wissing (Ferens Art Gallery - Hull UK)
I cannot find anything about her, but this article about her husband found here appears to mention her, "Sir Barrington Bourchier (1672-1700)
In April 1697, less than two years after his father's death, he was knighted by William III at Kensington Palace. He married Mary Crompton, daugther of Sir Francis Compton, Lieutenent-Colonel in the Horse Guards and a son of the 2nd Earl of Northampton.
But tragedy soon struck, Barrington's first son was buried in 1699, Barrington's brother, Mark, died in December the same year, only to quickly followed by his wife and second son and then by Sir Barriongton himself a few months later."
From bbc.co; spots removed throughout image with Photoshop by gogm.