Queen of the Kingdom of the Isles, her sister was the Queen of Iceland.
She swore to only marry the best knight in Britain, whom she perceived as Gawain. One of her vassals, Brian of the Isles, set out to defeat Gawain, thereby proving himself the best knight and earning the right to marry the Lady. Brian returned to the Kingdom claiming that he had slain Gawain, and the Lady prepared to marry him, but Gawain showed up on their wedding day and ended the marriage.
Source
Meriadeuc or Le Chevalier aux Deux Épées | c. 1225-1250