during world war i she traveled to belgium in disguise, several times, and was briefly a prisoner of the germans. she wrote about the war for "harper's magazine", "the boston pilot", and the "boston globe". she witnessed the burning of leuven, and worked with nurse edith clavell for a month. "she has suffered arrest in every country now at war, save serbia, where she has never been," reported one newspaper of o'reilly's war work. she flew above the chesapeake bay with the u. s. coast guard to report on their work in 1917. she lectured on her war experiences in the united states after 1917. after the war, she was especially concerned with the way false and lurid stories about german atrocities were circulating, and sought to correct what she called "the fakes". she also exposed "fake philanthropies" for war relief, often run by and targeting american women.