She appeared at the beginning of Episode Three calling with a request to see Rin. When Rin goes to meet her on the top floor of a building under construction, Yuria is dressed in a tattered maid's uniform, covered in blood and was clearly sick. Through her coughs, the girl is only able to say one cryptic sentence ("The flower of death! It's going to bloom in Tokyo!") before accidentally falling off the building and dying in front of Rin.
The whole thing might have ended there... IF several out-of-character aspects didn't turn-up upon Yuria's autopsy. First, although she appeared to be a wholesome schoolgirl, she seemed to be sporting several body piercings on her. It was also discovered that she was suffering from a disease known as "Higan" or the Equinox Disease, which was native only to Hagashima Island, or "Death Island", which would have killed her in a week if she hadn't fallen. Even stranger, when Yanagihara told Rin about this, he heard the coroner mention 'It can't be' - as if the coroner had saw this sort of thing before.
Later on, it was discovered she was acquainted with Sayara Yamanobe, possibly having a sexual relationship with the sadistic scientist. Sayara had infected the poor girl with Higan when Yuria had discovered Sayara's plans to cause a world-wide pandemic with the disease and to warn Rin about it.