What primary source or exquisitely researched academic work the name of Ranulph's wife? To my knowleddge Dugdaled did not cite a primary source for the scat information he research and wrote about in the latter 1600s. Where Dugdale drew his information, Eyton doesn't know. What is certain is she could not have been what we would think of as a "mistress" of William the Conqueror. Eyton makes this point quite clear, which the most 22 Feb 2021 FMG page now shows:
http://fmg.ac/Projects/MedLands/enguntps.htm#_Toc21095948
After the death of Duke Richard 1st, William was a child protected by devotees of Richard. Norman aristocrats sought for control, wealth, and status and tried to gain access to William to get it.