She is a middle-aged woman who dresses in black. She is described as being very "respectable, rather mournful, completely uninterested. She tends to be suspicious of foreigners, and so is hesitant to let Poirot in the first time he calls at End House.
Ellen is married to a man named William, who works in the garden at End House. They have a young son. When Nick Buckley made a will before her appendicitis operation, Ellen and William were the witnesses.
On the night of the murder, Ellen did not go out to watch the fireworks. She came into the hall just after Maggie Buckley had been found dead, and was surprised that Maggie had been shot. It is revealed that Ellen had had a premonition that something bad was going to happen, and deliberately stayed in the house that night, to see if anything did happen.
Ellen also tells Poirot that there is a secret compartment somewhere in End House. It is a sliding panel that reveals a little cupboard, about a foot square.