 Once the Visconti had conquered Milan, Squarcina Borri gave his daughter in marriage to Matteo I Visconti, Lord of Milan in 1269 to cement those bonds essential to maintaining the rule of the Visconti.Bonacossa and her husband co-founded of the chapel of St. Thomas in the Basilica of Sant'Eustorgio of Milan, where they were buried, along with their son Stefano and his two daughters Beatrice and Catherine, and the brother of Matteo, Uberto III Visconti.She died in Milan on 13 January 1321 .