Mary, Duchess of Hamilton
Mary, Duchess of Hamilton was buried on 12th May 1638 in the vault of the Countess of Buckingham on the north side of Henry VII's chapel in Westminster Abbey. There is nothing to mark her grave.
Lady Mary Feilding was a daughter of William, 1st Earl of Denbigh and his wife Susan (sister to George Villiers, 1st Duke of Buckingham). She was married at about nine years old to James, 3rd Marquis and later 1st Duke of Hamilton, politician. He was beheaded in 1649 for "invading England in a hostile manner". They had six children - Henrietta, Anne, Susanna, Charles, James and William, all except one dying young.
Charles, Earl of Arran was buried, aged about 10, on 30th April 1640 in the vault and Lord William was buried on 6th December 1638 in St Nicholas' chapel. Anne (1632-1716), suo jure Duchess of Hamilton, married William Douglas, 3rd Duke of Hamilton and had thirteen children (including Charles, Earl of Selkirk). Mary was a lady of the bedchamber to Queen Henrietta Maria and died at Wallingford House, Charing Cross.
Mary's brother Philip Feilding was buried on 19th January 1628 in the vault.
Further reading for her husband and daughter Anne
Oxford Dictionary of National Biography 2004