Sylvia Bassington-ffrench

Sylvia Bassington-ffrench is the wife of Henry and the mother of Thomas. She is an American heiress.

She knows the Draycotts, cousins of Frankie Derwent.

ITV's Agatha Christie's Marple
In the 2008 ITV adaptation, the character is morphed into one with a different name and backstory Sylvia Savage.