Fables comic books.
If you have read the comic books, you know that Cinderella managing a shoe shop is merely a front, and that her real profession is being a spy for Fabletown.
In the game, Bigby walks by her shop, and makes a small comment about the name choice, but nothing that seems to indicate he knows of her true profession (which is particularly odd, seeing as she works for him). And, seeing as there is a serial killer on the loose, having his secret spy help with the investigation is probably the most logical course of action.
Now, I'm not sure if the comics give a specific date for when Cindy joined the secret spy club, but surely we would have heard of her by now if she worked for Fabletown at this point in time? Do you guys think maybe this is the moment when she became the most badass spy in the story?
EDIT: Wait, the game takes place in 80's, right? Wasn't it aroung that time that Cindy was fighting Dorothy? Welp, there goes my theory. Nevermind, everyone.
EDIT2: Umm, this thread triple posted itself for some reason. If a mod sees this, can you please delete two of the versions so that there's only one left open? Thanks, and sorry.