The discomfort and righteous protectiveness of her husband suddenly fell away the moment Nymphadora realized who stood before her. She could curse herself for not having seen it earlier, but there wasn't time now. She whipped out her wand from her back pocket in a motion that was almost too quick to see, taking advantage of the few seconds Bellatrix gave her while getting her packages shrunk. Tonks' eyes were now utterly serious, the look of an Auror, and a formidable one at that.
"Bellatrix Black LeStrange. You might be blood, but you are also a wanted criminal. You can come with me peaceably or I will take you in by force." She might not have worn her ministers robes, but an Auror never truly took a day off and it's clear Tonks was ready to arrest Bellatrix on the spot. As for the possible fight to ensue, the crowd had begun to vanish from the street in fear of the possible show down. Maybe word would get back quick enough Tonks could get some back up, but she doubted it.