In the novel Appointment with Death, Mrs Boynton was the tyrannical matriarch of the Boynton family. She was the widow of Elmer Boynton and was the stepmother of his children. She had one biological daughter.
Appointment with Death (1988 film)
In the 1988 film adaption of Appointment with Death, Mrs Boynton was portrayed by American actress Piper Laurie. The character was given the first name Emily. Her husband Elmer is also mentioned. He died just before the events in the show. The portrayal of Mrs Boynton here is fairly faithful to the original, if a little less tyrannical and sadistic. In the original, Dr Gerard suggested that she was bored and so took a trip to the Holy Land for a new thrill. In this adaptation, there is a sideplot where Elmer had made a new will leaving some money to the children. Mrs Boynton intimidated Jefferson Cope into burning the new will (see his article for details). She then organised a holiday through Europe and the Holy Land to help them get over the death of the father.
Appointment with Death (2008 ITV adaptation)
In the 2008 ITV adaption of Appointment with Death, the character's backstory is changed. Here she has a first name Leonora and was formerly Mrs Pierce. At the time of the events in the show, she is married to Lord Boynton and so is known as Lady Boynton. Lady Boynton is portrayed by actress Cheryl Campbell.
In this adaptation Lady Boynton's money did not come from her current husband. She herself is not a former prison wardress but rather a wealthy financier and managed the Pierce Holding Company. The source of her wealth is not stated--it could have been her own money or that inherited from her former husband. Carol, Raymond are not her stepchildren but were adopted. Jinny is not her biological daughter but was also adopted. In addition, it is revealed towards the end that Jefferson Cope had also once been adopted into the family but was later rejected. Leonard is a stepson and the son of Lord Boynton.
In this adaptation, her cruelty is also portrayed as primarily comprising the beating and torturing of her adopted children--actions which were carried out on her instructions by one Nanny Taylor, a non-canonical additional character who is also present at the trip to Syria.
Lady Boyton is killed in a different way and for different motives, primarily as revenge by Dame Celia Westholme with Dr Gerard as an accomplice. Dame Celia said this was "to save" Jinny from Lady Boynton. There is an additional sideplot in which Jefferson Cope takes revenge on her successfully by destroying her financial empire. See here (click expand) for details.