While in the Ryzak solar system, (PROSE: The Secret Lives of Monsters) Journey was saved from a pursuing Dalek spaceship by the Twelfth Doctor when he materialised the TARDIS around her just seconds before her spaceship exploded. He was unable to save her brother, Kai Blue. He took her back to her command ship, the Aristotle. There, she saved his life, by convincing her uncle, Morgan Blue, that he could be useful.
Along with the Doctor and Clara Oswald, as well as two other soldiers named Ross and Gretchen Carlisle, Journey was shrunk using a moleculon nanoscaler. She and her teammates were then put inside a Dalek nicknamed "Rusty", inserted through his eyestalk. Rusty believed the Daleks themselves should be exterminated, so the operation which Journey participated in was conducted in an effort to discover how Rusty had become "good" and whether or not he could be repaired to aid in the resistance effort against the Daleks. Though several of Journey's teammates died after Rusty reactivated, she ultimately helped the Doctor and Clara to turn Rusty into rebelling against the Daleks.
Together with the Doctor and Clara, Journey was later returned to her normal size. As the Doctor and Clara prepared to leave in the TARDIS, she asked the Doctor if she could join him; he gently refused to take her, telling her that, although she was most likely very kind and brave, he did not want to travel with a soldier. (TV: Into the Dalek)
Behind the scenes
In the script of Into the Dalek, Journey Blue was described as being in her "early 20's".