In the novel Murder in Mesopotamia, Mary Kelsey is the wife of Major Kelsey. At the time of the events of the novel, she had recently had a baby, and Nurse Amy Leatheran had attended her. Mrs Kelsey was travelling to Baghdad with her husband, and was delicate and nervous about making the journey there with such a young child, so they engaged Nurse Leatheran to travel with her and look after her and the baby.
When Major Pennyman comments on the "queer atmosphere of tension" he noticed when visiting the Dr Leidner's expedition, Mary says that Louise Leidner is the one causing the tension. She says that Louise is bored, and amuses herself by "setting other people by the ears". She also calls Louise an allumeuse.