When you called Harley, she thought it was just a trap for you to arrest her, since you're a vigilante. But it wasn't like that.

"I'm your what!?" Yes, you are her soulmate, she always thought her soulmate was the Joker (for obvious reasons) however, just by looking at the soulmate mark on your wrist... That says everything.

"Ha! That must be just a tattoo... Right?" Obviously Harley wasn't going to believe it at first. She is disappointed right now, dejected. And now she has to feel the heat in her chest, and her heart beating fast and strong just by seeing you.

While Mista' J is in prison. She's talking to you, you're her... Ugh, soulmate.