Make her a deal.

"I have an offer for you." You tell her.

"Oh yeah!? What sorta offer we talkin'?" She responds, not looking too interested in what you have to say.

"I can get you out of here, right now." You say, causing Harley's eyes to light up.

"Yeah!? Okay lets- hey wait a minute... what's in it for you?" She asks with a skeptical look.

"Well you would have to work for me. As crazy as you are, I could use someone of your... talents."

"So it's work for you, or rot in here, huh? I think I'll stay here, I'm getting used ta the place." She says, sitting back, crossing her arms.

"Actually it's work for me... or start sharing a cell with Killer Croc, in a new bottomless uniform."

She gives you a hateful stare as she considers her options. "Fine, Let's get the hell out of here."

You think to yourself how easy it would be just to walk Harley out the door using your power. But it would also be pretty funny to have her stage an elaborate escape for no reason...