Harley's finger gun gesture references ... it seems as though this origin has been somewhat altered. Joker and Harley do indeed meet at Arkham Asylum, but rather than being a professional ...

Many of the inmates of comics' most infamous madhouse, Arkham ... A Gun" backup story, Batman struggles to fight back against his persona as it takes over his, seeking to finallu kill yhe Joker.

In the comics, Harleen Quinzel is a psychiatrist the Joker falls in love with while he's institutionalized at Arkham Asylum, and she becomes his partner in crime. The original movie, you'll recall ...