It seems definite that Sarah is the daughter of Hubert de Montcanisy (Munchesny) but it's not clear which Hubert; Hubert I who married Muriel Valoingnes as his second wife, or ,his son Herbert II from an earlier marriage,
The dates are all out quite a bit including Sarah's as her son who inherited as a minor, didn't reach his majority until 1186, This would place his birth about ca. 1165 or slightly later, which makes Sarah's birth date of 1117 pretty unlikely.
This may mean she is more likely to be the daughter of Herbert II, but probably needs some more research before making that change.