Guillaume de Grandmesnil - Guillame de Grandmesnil father of Pernel de Grandmesnil

Agreed, but not this William. My notes say:

She has long been known to have been a great granddaugter of Hugh de Grentmesnil, the Domesday tenant. She was formerly believed to have been a daughter of either Hugues II de Grentmesnil or his brother Yves II. Her father is now known to have been Guillaume II de Grentmesnil.

Petronille de Grandmesnil