10 Most Heroic Things Harley Quinn Has Ever Done
2. Saves Poison Ivy - Batman #41-43
DC has recently been trying to backtrack on Harley and Ivy's relationship, for reasons that I cannot fathom seeing as how there is no way they could handle this and NOT get rightly yelled at by readers, so why even do it at all? Especially when just a few years ago, Tom King spent a whole storyline detailing why their relationship is so important. If it wasn't for Harley, Ivy would have literally ended the world.
Ivy, for various reasons that had led up to this moment, has finally gotten fed up with humanity's nonsense and has taken full control of the green in order to conquer the world through mass mind control. Only Batman, Catwoman, and Harley are unaffected by the end of it, and Batman realizes that he has NO idea how to fix this.
Fortunately, Harley does, managing to get to Ivy and talk her down. Not by psychoanalyzing her or beating her up, but by simply showing Ivy the compassion that can only be given to someone hurting the way Ivy is hurting by someone who is hurting the same way.
They're both hurting, so they can at least hurt together.