In August 1982, Ang responded to an appeal for medical personnel from Christian Aid to treat war casualties in Lebanon and went to work at the Gaza Hospital near the Sabra and Shatila refugee camp in Beirut. The following month, she became witness to the Sabra-Shatila massacre during the Israeli invasion of Lebanon in 1982. She and two other hospital staff testified to Israeli Kahan Commission on the Sabra and Shatila massacre on September 1982.