The daughter of Refr hinn mikill ("the Great") and Finna, "Steinunn was both descended from and married into a powerful family of priest-chieftains (goðar)". She is Hofgarða-Refr Gestsson's mother.
Brennu-Njáls saga (102) relates that she preached heathenism to Þangbrandr, a missionary sent to Iceland by king of Norway Óláfr Tryggvason, trying to demonstrate Thor's superiority over Christ ("Have you heard," she said, "that Thor challenged Christ to a duel and that Christ didn't dare to fight with him?"). On this occasion she composed two skaldic stanzas (lausavísur) in which she attributes Þangbrandr's shipwreck to Thor. These verses are one of the few testimonies of pre-Christian skaldic poetry composed by a woman that has come down to us. They are also preserved in Kristni saga (9) and Óláfs saga Tryggvasonar en mesta (216).