Her paternal grandmother Isabella survived her brother Walter VI of Brienne, titular Duke of Athens etc., who died without issue at the Battle of Poitiers in 1356.

However, Peter died childless in 1384 and was succeeded by Mary and her husband, Raimondo del Balzo Orsini di Nola, whom she married in Taranto the same year.

She stayed in her castles of Lecce and Copertino when Raimondo travelled and served the king against the papal troops and the supporters of the junior Angevin line.

After her husband's death, she was besieged in Taranto (1406) and resisted the troops of Ladislaus for months, until he triumphed and imprisoned her and her children, demanding she marry him.

In 1444 she witnessed the marriage of her granddaughter Isabella of Clermont, daughter of Tristan and Catherine and heiress to considerable feudal estates in Southern Italy, to Ferdinand of Aragon.