Continuity mistake: When we first meet Harley Quinn, her gloves are white before becoming their normal colors of black and red in the next shot.
Continuity mistake: The Joker reads “Charles Michael Collins” from Charlie’s card, but later, when he shows it to the camera, there is no middle name on it.
Factual error: The note the Joker has that says Charlie has changed his name to Don Wallace lists his address as 12 Marigold Lane, Springdale, Ohio, a city near Cincinnati; however his area code is listed as 614, which is the Columbus, Ohio area code.
Answer: She escaped off-screen and created a copy of herself to fool everyone.