The daughter of Patrick Desmond Carl-Alexander Guinness and his first wife, Liz Casey, she was educated at St. Columba's College, Rathfarnham, near Dublin.

She and Gawain O'Dare Rainey were engaged on 31 January 2005. He is the son of Michael O'Dare Rainey and his former wife, the Hon. Jane Ormsby-Gore, eldest daughter of the 5th Lord Harlech. On 1st July 2006, Guinness and Rainey were married in Leixlip, Ireland. The wedding was extensively covered in "Hello" magazine (18 July 2006) and was attended by 500 guests, including Jasper Conran, Mario Testino, Paddy Moloney, Angelica Huston, Jacquetta Wheeler, Jade Parfitt, Erin O'Connor, Garech Browne and Philip Treacy. She has two sons by Rainey, one born in 2001 and one born in 2006.

A portrait of her is held at the National Portrait Gallery in London.

--Wikipedia