Don't know what she looks like today; I'm remembering her from the Scary Movie franchise and My Super Ex-Girlfriend movie.
Blonde-haired, athletic and with a strange propensity to portray actresses who for some reason have greatly unexpected physical strength but a bit of ... mental imbalance.
Even demonstrates the thoughtless, non-malicious brand of cruelty that sometimes characterizes Harley. Scary Movie was full of such scenes. Super Ex featured at least one or two as well. Overall impression is of a semi-comical, surprisingly formidable, dangerous-without-actually-possessing-true-malice ... lunatic.
That way when Batman Beech slaps her people will be like 'OMG THANK YOU!'
But in all seriousness - It is difficult to find the best IMO. Cause with me I try to think of someone who can pull off her voice yet still be sexy at the same time. I thought maybe Milla Jovovich but I dont see her doing the Voice though I think she can pull the 'Look' off easily.
I think she would a great character for another origin story, despite the fact that Ledgers Joker is gone. The Batman movies, save for the Bale stories, have never been a linear storyline, so why not create a story for her. I know she played Rachel in Dark Night, but Maggie Gyllenhall is an amazing actress who would bring many layers to the Character. We tend to think of dramatic actresses for these roles, by why not some talented comedic actresses?