Otway-Ruthven's area of particular interest was Ireland in the twelfth century and the impact on the country of the arrival of the Anglo-Normans. She published extensively and her monograph "A history of medieval Ireland", was a landmark in Irish historiography. She translated the Cambridgeshire Domesday Book in 1941 and the "Liber Primus Kilkenniensis"., she published Dowdall deeds with Charles McNeill in 1960 and brought a calendar of the Talbot de Malahide papers close to completion.