My version of a real-world The Dark Knight based Harley Quinn. My Harley would be a Gotham University grad student writing her psychology dissertation on the Joker. She's near her mental breaking point, when one night one of Joker's goons attempt to assault and mug her, and she kills him by accident. This causes her to suffer a psychotic break, and the Joker, seeing her criminal potential, takes her under his (broken) wing, molding her into--Harley Quinn!

I love the bold black and red jester outfit, but as others have already pointed out, it wouldn't translate very well to a real world aesthetic. She still wears black and red, but the red is dried blood on white fabric. Instead of carrying a cartoony mallet, she carries a hammer, which she gleefully uses to bash individual heads in.

Anyway, that's my take on her.
She definitely keeps the pigtails.