Complex sentence: It is in this context that Madeleine Pauliac was appointed in April 1945, French chief doctor of the hospital of Warsaw in ruins, and responsible for the repatriation mission at the head of the French Red Cross.
Split into simpler sentences: It is in this context that Madeleine Pauliac was appointed, in April 1945, chief doctor of the hospital of Warsaw, which was in ruins. In this capacity she was responsible for the repatriation mission at the head of the French Red Cross.