Biography
Charlotte was the youngest daughter of Strackman Lux's grandfather, who built his dying daughter The Library and its hard drive to contain and embody her living mind, and a doctor moon to maintain The Library and her spiritual wellbeing (the latter task though its personification in Dr Moon).
In her perpetual dream, she describes to Dr Moon a world that she sees when she closes her eyes; a world that is later shown to be The Library.
In the world of The Library, the Girl is seen as a floating metal sphere that turns off and falls to the floor when the Girl opens her eyes on Earth. While Tenth Doctor and Donna were in the Library, they came across this metal sphere, which the Doctor identified as being a security camera, although he told Donna after examining it that it was indeed alive.
The Girl came into contact with the Doctor through her television screen, where they engaged in a brief conversation which was ended when the technology malfunctioned.
Shortly after this encounter with the Doctor, Dr Moon came to have a talk with the Girl alone. Here, he told her that there were differences between the Real World, and the World of Nightmares. When the Little Girl said that she already knew this, Dr Moon shocked her by telling her that the Real World was false, and the World of Nightmares was real. He told the Girl that the people inside 'her' Library were very real, and that they needed her help.
The Little Girl then proceeded to 'save' Donna Noble, uploading her to her hard drive. She also did the same with those members of River Song's crew who were killed by the Vashta Nerada, although data corruption resulted in Miss Evangelista's face being disfigured (although her intelligence was boosted). Eventually, the Doctor and River Song realize that what happened to Donna also happened to the more than 4,000 humans who were "saved" by CAL in order to protect them from the initial Vashda Nerada attack a century earlier. River Song sacrifices herself to allow these people to be "downloaded", and the Doctor later stabilizes CAL's systems. In return, CAL provides a final home for the consciousnesses of River Song and her crew. (DW: Silence in the Library/ Forest of the Dead)