Mabel went to Setbia as a nursing orderly during the First World War when her husband volunteered to serve there as chaplain to a Red Cross Ambulance Unit. Mabel contracted Typhoid and died of Pneumonia on 11th July 1915, shortly before the death of her younger son, Christopher, from wounds sustained at Gallipoli where he served with the Royal Naval Air Service. Mabel is buried in Kragujevac Cemetery in Serbia, alongside Dr. Elizabeth Ross and Nurse Lorna Ferriss. Mabel's letters 'Letters from a Field Hospital' were published after her death and are available to read on the Internet - https://archive.org/details/lettersfromfield00dear
I wonder if there will be a stamp issued to commemorate Mabel Dearmer as there has recently been by the Serbians to commemorate some of the other women who went to help Serbia during WW1 - Flora Sandes, who was a soldier with the Serbian Army, Evelina Haverfield, Dr. Elsie Inglis, Dr. Elizabeth Ross, Dr. Katherine McPhail and Dr. Elmslie Hutton.
For an in-depth discussion about the life and work of Mabel Dearmer, Dr. Margaret Stetz in America sent me this link to the excellent work of Diana Maltz of Southern Oregon University: