Yes, technically these three have all been villains at one point or another, but they've also been heroes too. In fact, in the wake of Bruce Wayne "dying", Catwoman, Poison Ivy, and Harley Quinn all teamed up to do some "good" in Gotham. And that they did.
While this may not have worked at one time in their pasts, their desire to "break away" from their pasts was what brought them together. Yes, they stumbled, but they made it work for a while. And even as individuals, all three have had heroic exploits, and have worked positively with Batman.