In 1908 Constance was accepted by the
Church Missionary Society (C.M.S.) and sent out to
Kampala,
Uganda, where she worked in the
Mengo Hospital, under Dr Sir
Albert Ruskin Cook. Albert Cook was a contemporary at
Trinity College, Cambridge of her brother, Arthur Norman Watney, so they may have met through him. In 1917 Mengo hospital, in addition to its missionary work, served as a base hospital for the fighting in
East Africa, and for her share of the very heavy work, "Sister Connie", as she was called, received the
MBE in 1918. For nursing an official of the Belgian Government, Sister Connie was awarded the honour of Croix de l’Ordre de la Couronne (
Order of the Crown (Seventh Class). In May 1921, Watney joined
Dr Algernon Stanley Smith (who had been brought up by Constance's maiden aunts, Alice and Emily Watney in South Croydon after the death of his mother when he was only one year old) and Dr Len Sharp at
Kabale, southwest Uganda, where they a new beginning was made for missionary work into
Ruanda, in Belgian territory. She helped to start a hospital at a place called Kabira, where she was the first matron, under very difficult conditions and they were able to receive the first patient in June 1922. The first building had 12 beds but then expanded to 50 when the hospital was officially opened in 1922. In 1923 there were 73 beds for men, 40 for women; in that year they had 705 inpatients and conducted 181 operations. ==Invalided home==