Florie Punt
Ooookay. Insofar as my fried brain can generate words, I have a basic idea:
Florie has four siblings in a working class household. The slums. Lives with a strict, disciplinarian mother. Seeks refuge in rebellion. Runs away. Petty scammer. Runs into a "Professor" LaBlanche, a tall, spectral and icy man (who I envision as gay, but not exactly open about it) who plays the part of her uncle. She acted as confederate in a fake séance act which traveled around Great Britain. Whether actually French or not, LaBlanche could speak it like a native and over the next few years, he made sure to immerse her in the language by speaking it all the time.
Why, for Florie, an advantage of speaking French over English? So she could hide her working class accent, which, as herself, she would have difficulty doing. The fake French accent enable her to sound "proper".
One to three years ago, Flroie had a falling-out with LaBlanche (kind of a jerk) or something, leaving her on her own.