She took her BA and MA at the National University of Ireland in Cork, and her doctorate at the University of Basel. She taught at the University of Reading until 1988, whereupon she was appointed to the German fellowship at Exeter College, Oxford: a post she still holds. In 2007 she was the Mellon Distinguished Visiting Professor at the University of Illinois.
Her father was the Professor Michael J. O'Kelly, the distinguished Professor of Archaeology and Irish Pre-History at the University of Cork, who discovered the midwinter illumination of Newgrange in 1967.