James waited until Bob confirmed she was negated and then made his way through the crowd, closer to them both. Then he just had to follow them. The good thing about following someone who was following someone else - her focus was somewhere else. There was practically no chance that she would notice someone tailing her.
Once they were alone, James started to move forward in order to subdue her. Her words nearly triggered him - she was one of them, just like the scientists. But worse. Worse because she was a mutant. She was doing this to her own people. On purpose. She was enjoying this. He managed to push the feeling down, keep himself from turning into a beast and tear her throat out. But he paused when she began dancing around. Smart girl.
While she was distracted speaking to Bob, he moved up behind her quickly and quietly. Even without activating his abilities, he was fairly silent when he moved. In a sudden flurry of movement, he rushed her, knocking her hard on the back of the head so she'd stumble back into negation area. Following her with sure footing, he caught her around the neck from behind, choking her so she couldn't speak and so she'd lose consciousness soon. "It's better if you don't fight," he whispered into her ear, echoing her own warning only moments before.