1820 print of Isabella, Countess of Sefton, Charlotte Mordaunt (née Musgrave), and Henrietta, Lady Morris (née Musgrave) by Samuel William Reynolds after Sir Joshua Reynolds
Isabella (Belle) Stanhope's article in the peerage is here. Charlotte Mordaunt's article in thepeerage is here Lady Morris' article in thepeerage is here. A print from this set for Maria, Duchess of Gloucester is here and a portrait of Countess Isabella is here.
From Wikimedia; sepia tone removed by gogm. The originals are at the National Portrait Gallery in London.