In this story, Harley is an accomplice to the murder of Jason Todd. Harley may not have been the headline of Jason's murder, but her presence is undeniably there, and Joker would profess it to you for days on end. She'd do anything to please her Puddin', and if that means helping him beat the crap out of Batman's beloved sidekick... hell, who wouldn't want to please a man just by beating up some kid? Sounds like a great first date! Harley isn't around during the Gotham Contract, but her presence lingers just as much as Joker's does in the journey Batman must take to overcome his inner demons.

Absolutely go for Margot Robbie's Harley. If you want, you modify it with some Tara Strong or even Harley's original voice actor, Arleen Sorkin. Honestly, as long as you can nail a New Jersey or Brooklyn accent and sound sadistic while using it, then you're a great contender.

Since Harley's appearance is relegated merely to Jason's death, her performance is only a little under Joker's. It's an exciting night for them both; why not enjoy it?

Harley references:

https://youtu.be/vA8ek62E2K4?t=3m31s Some good dialogue to help you detect her accent and personality.