She was named after her maternal grandmother, Oona O'Neill Chaplin.
During her time there, she appeared in several school plays, touring the United Kingdom in an adaptation of Romeo and Juliet and impersonating her grandfather in the role of Bottom in an adaptation of A Midsummer Night's Dream, which was performed at the Edinburgh Festival Fringe.
Following the marriage, O'Neill gave up her career plans.
She and Chaplin had eight children together and remained married until his death in 1977.
From the moment she turns up at the 1883 shoot she is raring to go: endlessly smiling, incurably affable and seamlessly moving between French and English with impressive ease.
Her bilingual rapport with the team is the only clue to her illustrious heritage and cross cultural upbringing.