This marriage had been pre-determined by the Treaty of Viterbo in May 1267 between Charles, the exiled Baldwin II of Constantinople and Isabella's father.

In line with the treaty, on the death of Isabella's father William, in 1278, it was her father-in-law Charles who succeeded to the throne of Achaea.

The peace lasted until 1293, when the Greeks retook Kalamata; Florent's emissaries, however, persuaded Andronikos II Palaiologos to return it.

On Philip of Taranto's death in 1313, Isabella's daughter by Florent, Matilda of Hainaut, became Princess of Achaea.

Her life was the inspiration for Princess Isabeau [el] (Πριγκιπέσσα Ιζαμπώ), a novel by the Greek writer Angelos Terzakis, originally serialized in the Kathimerini newspaper in 1937–38.