@TalionRarshak short answer: she's a war refugee who made it back to Japan, but she's got so much PTSD that she's fucked in the head and has flashbacks' dreams, and memories of things that didn't happen.
Longer answer: for sure she was in Ariehen with her mother at the time it was attacked, her mother did die, the two comedians were from people she saw on television, "Tanaka" and some of the others were people from the UN camp prior to returning to Japan. As for the others, Nishi and Hagashi were likely a composite of people made up from her imagination from things she had heard and people she'd seen. Her back-story is the kind that is like "standard ruined girl" from any tv show or movie, which is how she saw herself. She was experiencing severe psychosis brought on by PTSD