Emily (Mad Dogs and Englishmen)

Emily was an old woman who Fitz Kreiner found sleeping at a table deep in the TARDIS library, surrounded by hundreds of books about British birds. She was dressed in teenagers' clothes from the 1960s and covered in cobwebs. When Fitz brought her to the Eighth Doctor in the console room, the Doctor recognised her and seemed embarrassed. She didn't recognise the Doctor. (PROSE: Mad Dogs and Englishmen)

Behind the scenes

 * Though left unstated, the clear implication is that Emily entered the Doctor's TARDIS as a teenager and got lost in its infinite corridors, living out her life inside the ship. As her clothes are specified to be reminiscent of the 1960s, she appears to have been a classmate of Susan Foreman's.