'Thrillkiller '62' is an Elseworlds graphic novel that reimagined all the players in Gotham City, with a primary focus on Batgirl/Barbara Gordon. Published in 1998, it is a sequel to the Elseworlds story 'Thrillkiller.'
But we're not here to talk about Batgirl. We're here to talk about Harley Quinn! Harley was also reimagined in Thrillkiller '62, written by Howard Chaykin with art by Dan Brereton: