Having checked several printed sources and the general internet for information on the mother of Philippa and Catherine de Roet and/or the wife of Payne de Roet, I have found nothing on her identity. The only sources for Catherine of Hainault being that person are several World Connect data bases-and they do not indicate a source. That does not mean that they are wrong.
One point in favor of a connection between the Roet's Catherine of Hainault (sister of Edward III's consort Queen Philippa) is that the Payne, Philippa, and Catherine Roet were at one time or another in Queen Philippa's household.