Turton has Guilla, daughter of Boniface, marrying both Oberto I Marquis of Este, Count of Milan (912-975) and Umberto Marquis of Tuscany (?-961), with children by both husbands. Since both husbands lived past the dates of her children's births and there is no explanation such as divorce, it makes it doubtful that the same Guilla married both.
A posting in soc.genealogy.medieval indicates the presence of another Guilla, son of Theubaldus who was son of Boniface. Although the posting does not indicate that Guilla m. Oberto, this may well be the Guilla who m. Oberto I Marquis of Este.