Mentioned in "Stolen Car": Finding herself suddenly in modern-day Paris, Charlotte was extremely disoriented, wandering the streets for about a week. She managed to sell her now-antique coins for modern currency and bought a boat ticket to England. So few people travel internationally by boat nowadays that they didn't check her for I.D. and stuff. Yeah. Real vigilant border police.
Still believing herself to be either hallucinating or in hell, Charlotte headed for the nearest hospital to be examined. There she met Dr. Chris Taylor and his murderous stalker of a brother, Alec. She managed to convince Alec to leave, then asked Dr. Taylor where she could stay for the night. He directed her to a hotel and told her what I.D. was. ("Stolen Car")
Charlotte got a job as a Starbucks barista but was soon captured by the Daleks along with Robin Terrell, Becca LaFaye, Yalti Lythis, and Dakota Hemmel. The Daleks were searching for the Doctor and demanded that the captives turn him over to them in exchange for their freedom. Charlotte had no idea what they were talking about as she hadn't met the Doctor yet and thus was released. ("The dream that no one dreamed")
Some time later, Charlotte ran into Becca and Robin again, this time along with the Fifth Doctor. She was told by the Silence to kill the Doctor but did not act on that subliminal order as she only knew the Doctor as "Celery Man". ("The Sound of Silence")
Charlotte's boss, Mr. Merrick, was stabbed under unusual circumstances about a month later, and Charlotte decided to try and help with the investigation - mostly to prove her innocence, as it was well-known at work that she carried a knife. The Anonymous Chicken Detective Agency - Nate Stevens with a cybernetic eye, Lionel the Cat, and Sophie Smith - were in charge of the investigation with the (questionable) help of Robin, Darren Hughes, and Tyra. She was prodded into revealing choice details about a "previous life" upon accidentally stabbing her dead boss's corpse. It's complicated. ("Forever Changing")
Fueled by a desire to see if her final letter to her father (fic: "Almost Last Words") was delivered, Charlotte went searching for a book of her compiled writings, bringing her to a (modern-day) library infested strange glittering walls, time corruption, and Captain Jack Harkness. Whom she fancies a bit. But then again, who doesn't? But perhaps she herself has something to do with the corruption and Reapers everywhere... and the mysterious Daathvaen awakening in the shadows. For the first time, she tells the truth about her past when confronted by Jack.("Shadows Awaken")
After those adventures, Charlotte was fired by her new boss for repeated absence. Quite frustrated, she soon saw the TARDIS and, following it, tripped on the Fourth Doctor's scarf. The Fourth Doctor seems to remember her face... instead of telling the truth, she opens the TARDIS and is overwhelmed by what she sees. The Doctor introduces himself, Charlotte briefly pulls her knife on him due to Silence triggering, and Four quickly deduces that she is Charlotte Corday. He offers her a deal: she and he can travel anywhere they want, to as many places as they want, but at the end of it all, she has to return to the Reign of Terror and be beheaded, to preserve history ("L'Ange de l'Assassinat")