She accompanied her husband on the Eighth Crusade against Tunis. On their way home, they stopped in Cosenza, Calabria. Six months pregnant with her fifth child, on 11 January 1271 she suffered a fall from her horse after they had resumed the trip back to France. Isabella gave birth to a premature stillborn son. She never recovered from her injuries and the childbirth, and died seventeen days later, on 28 January. Her husband took her body and their stillborn son and, when he finally returned to France, buried her in Saint Denis Basilica. Her tomb, like many others, was desecrated during the French Revolution in 1793.