According to her article in thepeerage, "Charlotte Elizabeth Boyle, Baroness Clifford was born on 27 October 1731." She married in 1748, bore four children who reached adulthood, and died in 1754 at the age of 23. She was Dorothy Boyle's younger sister. Her son William became 5th Duke of Devonshire and married Lady Georgiana Spencer and then Lady Elizabeth Hervey.
From bbc.co; image made lighter by gogm.