I have already built a Harley Quinn character for pfs. But mine got it's inspiration from the Suicide Squad comics and not the movie. But once she hits lvl 12 (she's lvl 9 now and is a lot of fun to play) I will try to build another one with the movie character as my inspiration.
My current Harley Quinn is a Barbarian 8/Unchained Rogue 3 with another lvl of Barbarian as the last one.
Her Stats are:
(I didn't want to dump wisdom because of reasons but I also wantet to boost her charisma so I had to dump int...)
As a weapon I use the Earth Breaker.
And you have a lot of roleplay options. You don't have to be the crazy psychopath who wants to murder everyone. I'm always trying to play her crazy but at the same time reasonable.
And always remember, Harley Quinn is highly intelligent yet highly unpredictable. So just have fun and, as Mitch already said, cooperate with your group.