Two entries with the name Guendoloena.
Guendoloena
Merlin’s wife in Vita Merlini and a flower-maiden.
A beautiful Welsh woman, she despaired after Merlin went mad at the battle of Arfderydd. In one of his moments of rationality, Merlin sent a message to Guendoloena, telling her to give him up and to remarry. He lapsed back into insanity, however, came to Guendoloena’s wedding, and killed her prospective husband with a pair of stag’s horns.
She may be identical with Chwimleian, mentioned in Afollonau, one of the Welsh Myrddin poems, although she may also be identified with that other famous Welsh flower-maiden, Blodeuwedd. It seems quite likely that this Guendoloena is an immediate forerunner of the ill-fated Guinevere of the later Arthurian cycle.
Source
Vita Merlini | Geoffrey of Monmouth, c. 1150
Guendoloena
Gwendoloena
Arthur’s queen in De Ortu Waluuanii, probably a variation of Guinevere.
Unique to this story, she is given prophetic powers which allow her to predict Gawain’s arrival at court.
Source
De Ortu Waluuanii Nepotis Arturi | Late 13th century