This looks to be a scene from one of the short fictions scattered throughout the books, I don't remember which right off.
In this scene the Acanthus wearing the Union Jack dress was working as a DJ in a club when she used her magic against a man in the crowd. I don't remember it being rich on details but whatever she was doing had her questioning whether it was right, while justifying herself based on what he had done.
It was a scene of a Mage pushing her ethical limits to stop someone who had broken those limits.
Very appropriate for the topic of this book....