Further training was interrupted when in late 1918 she joined a mission to Poland, as Medical Officer for the British Typhus Unit. She also worked with the American YMCA assisting the Polish Army and POW department in stemming infectious diseases in her father's ancestral town of Chrzanów. The health of the children was a major influence on her later career as she speculated about the different outcomes in spite of their traumatic experiences. Lowenfeld returned to England briefly as war broke out between Poland and Russia. She went on to Warsaw to set up a medical department for prisoners of war and worked on improving sanitation and undertook refugee work.