Arthur’s sister in Wolfram’s Parzival, replacing Anna from Geoffrey of Monmouth and predating Morcades or Morgause. Der Pleier calls her Seife.
She was the daughter of Uther Pendragon and Arnive, the husband of Lot, and the mother of Gawain, Beacurs, Itonje, Cundrie, and Soredamor.
With her mother and daughters, she was trapped in the Castle of Marvels for many years, under the enchantment of the sorcerer Clinschor (Klingsor), until rescued by her son Gawain. Lot was dead by the time she was freed, so she married Florant “the Turkoyt” of Itolac.
Source
Parzival | Wolfram von Eschenbach, 1200–1210