In the novel A Murder is Announced, Nurse Ellerton was a nurse working in St. Mary Mead. She committed two “mercy killings” using morphia, and inherited large sums of money from each patient.
Nurse Ellerton doesn't appear in the novel, but is mentioned by Miss Marple. Miss Marple does not state who Nurse Ellerton is a parallel of, but Diana Harmon was of the opinion that she is a parallel to Dora Bunner.