An undated charter records an agreement between "Willelmum de Filgeriis filium Henrici de Filgeriis" and "Eudonem filium comitis et Gaufridum de Castro Brientii et Willelmum de Guirchia" relating to the marriage of “Gaufridi de Filgeriis” and “filia prædicti Eudonis filii comitis”. The primary source which confirms her name has not yet been identified.
Mathilde married Seigneur Geoffroy DE FOUGÈRES, son of Seigneur Guillaume DE FOUGÈRES and Agatha DU HOMMET. (Geoffroy DE FOUGÈRES was born in Fougères, Ille-et-Vilaine, Bretagne, France and died on 14 Jun 1212.)