In the novel Lord Edgware Dies, Rachel Dortheimer is the daughter of Mr and Mrs Dortheimer, and an acquaintance of Captain Ronald Marsh.
According to Captain Marsh, Rachel is dark, and has a "long Jewish nose".
On the evening of the murder, Captain Marsh dines with the Dortheimers, attends the opera with them, and has supper with them afterwards, and he and Rachel dance.