So she gets angry with Penguin's comments. Last time I checked, emotions weren't illegal.
It's simple. Batman was illegally assaulting Penguin. Regardless of Penguin's current legal status, that isn't something he has a right to do. Even if Penguin is a child rapist, Batman has no right to attack him and Romy is required to defend him.
He refused an order from the police. He didn't move when ordered as legally required and kept his hands consealed. The order 'Hands up' or 'Where we can see them' is given for a reason. If you reach for something the police cannot see, they are legally allowed to shoot. And it really ought to be common knowledge that Batman carries an arsenal of weapons, even if they don't know what they are exact.
In alot of ways, the belt makes things worse. She knows that he has weapons, but not what those weapons are. A known 'unknown' that puts her in fear for her safety.
Lastly and most important, he's *Batman*. How dangerous he is should be common knowledge by now. Had it been say, Killer Croc, should she have waited untol 300 pounds of muscle was bearing down on her? Or when he's made it clear that he won't come peacefully, take the only advantage she's got?