I simply love this story. It seems like you've nailed all the characters, dialog and all, aside from a little bit on Ivy's part (I don't think she would eat soup made from a plant).
Aside from the un-detailed continued romps of Harley and Dean, Chapter 1 was perfect.
Chapter 2 had a fine lead-up while keeping Ivy in character (aside from the former complaint). But I was expecting a little more creativity with Ivy's powers.
Chapter 3, while lacking in the good stuff, was a brilliant injection of storyline. Penguin was perfect, and the whole scene really flowed.
Keep up the good work. I can't wait to read more (if you do intend to continue).