I mean this is the least dickish and most genuine way, but I really don't see how they could arrest Violet, honestly. Unless they got her while she was asleep, and then there's the problem of them having to not wake her up, and if they took her bracers off, which would make sense since they could be used as weapons, she'd just float away. If they just shot at her, especially non-lethal, it would take some well aimed shots to knock her out, and just trying to grab her wouldn't really work either... Did they run her over with a truck or something?
Also... Luna and Violet are female, but who's the third female in the cell? JJ? Where did Ashton go or is he removed now? What about the people in the Hills?