[5] Upon William's murder on 6 June 1333, she became the sole legal heir to all the de Burgh lands in Ireland.

As Countess of Ulster, she was raised in England and married Lionel of Antwerp, 1st Duke of Clarence, on 15 August 1352 at the Tower of London.

Elizabeth's daughter Philippa succeeded as Countess of Ulster, and married Edmund Mortimer, 3rd Earl of March, in 1368.

The House of York would base its claim to the English throne on their descent from Lionel of Antwerp.

She was buried at Bruisyard Abbey, Suffolk; as her body was being repatriated, her husband obtained royal approval for her mother's new foundation of Franciscan nuns there.