This is the tomb of Penelope Boothby, who died in 1791, aged 6. Her father, Sir Brooke Boothby, was a significant figure in the history of the Enlightenment- the first publisher of Rousseau's Confessions and a colleague of Erasmus Darwin's. He idolised his daughter, raised her according to Rousseau's principles and was utterly devastated by her death.
Penelope was painted by Reynolds and (posthumously) by Fuseli. The effigy on her tomb is by Thomas Banks.
"She was in form and intellect most exquisite. The unfortunate Parents ventured their all on the frail Bark. And the wreck was total"