FMG updated the "England, Kings 1066-1837" webpage on 29 Oct 2021.
About this person profile, it shows:
"4. MATHILDE de Normandie (-26 Apr ----). The necrology of Saint-Nicaise de Meulan records the death "VI Kal Mai" of "Mathildis filia Willelmi regis Anglorum"[68]. She is not named as a daughter of King William by either William of Malmesbury or Orderic Vitalis. There is no basis for assessing her order of birth among the other known daughters of the king. An undated manuscript names "Mathildem Anglorum reginam, nostri cœnobii fondatricem, Adilidem, Mathildem, Constantiam, filias eius" heading the list of the names of nuns at the abbey [69]."
http://fmg.ac/Projects/MedLands/ENGLAND,%20Kings%201066-1603.htm#Wi...
Cawley sources "Mathilde de Normandie" as a nun "at the abbey." Though he doesn't specify the abbey, Cecilia was an abbess at L'abbaye de la Sainte Trinité, Caen, Haute-Normandie. Perhaps Matilda or Mathilde was a nun at the same abbey.
