1759-1760 Charlotte, Lady Maynard (c.1731-1762), née Bishopp by Sir Joshua Reynolds (Hunterian Museum, University of Glasgow - Glasgow UK)
Her article in thepeerage is here. She married the fourth Baronet Maynard of Walthamstow, Sir William Maynard. She bore one child, Charles, who became the fifth Baronet.
From bbc.co; image lightened to bring out details.