Madeleine is a non-canonical character who was created for the ITV's 2010 adaptation of The Secret of Chimneys. She is the wife of Lord Caterham and the mother of Bundle and (in this adaptation only) Virginia Revel. In the original novel, Lord Caterham's wife is not named. Madeleine is already dead at the time of the events in the episode and is seen only in several flashbacks to events during a former houe party at Chimneys in 1932, some 23 years earlier.
The actresss who portrayed Madeleine is not listed in the credits but IMDB reports that it is Nicci Brighten.