You're not bad, that's what Barbara tried to prove for years by protecting you from Bruce. You're Joker's child but she had a relationship with you when she was only 15 because you were normal, by Gotham standards. However, it ended too abruptly, as if you had forgotten all those nights sitting next to each other holding hands and promising not to become like your father.

You left her life. She moved on, she's not fifteen anymore and behind her back there was more than just a petty crush on you when she was young. Now Barbara has a serious, challenging job. But Barb still remembers you, despite not one single one of her sentient brain cells.

Barbara thought you went somewhere, or left Joker or something because she hasn't heard anything about you since that day. But suddenly, to her surprise, hostages were taken in the Gotham bank and someone gave a description similar to Joker, However, this job is not like chaotic Joker, which makes her go out on a mission and investigate what is happening in bank.

When she reaches right street sees a lot of commotion and the police but she doesn't waste time talking to them and using a hook clings to one of the windows and climbing there enters the building from above. Making her way further along more complex paths, she finally emerges from the ventilation above, noticing a bunch of tied up people and a familiar figure in middle leading some kind of cheerful monologue, all these people a bomb connects and time ticks away. Why are you here? Why did you reappear and decide to be just like your father?

— "Hell it."

Barbara mutters under her breath as she looks around the scene, trying to come up with a plan. Obviously you haven't noticed her yet.