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As the text on this page makes clear she was the wife of Hugh not William.
The book on the Malbons, says Hugh married a Petronilla but this one de Vermandois (daughter of Peter Vermandois).
Although this page which she was a Scudamore (sometimes confused with Vermandois) but one with different parents to the ones named here:
http://knight-france.com/geneal/names/3010.htm
So, while there is a difference on who she was, there seems to be a consensus that Hugh married a Petronilla and that he was the son of William and a Adelicia or Adelia.
Are there any sources to suggest otherwise?
On that front we seem to have:
A duplicate: Petronilla Scudmore
An awfully similar profile (same mother, different birth date, different husband): Petronilla Scudmore