I came up with what I think is a good idea. I'm going to let my oldest hold her camera in her hands facing forward and on(not looking through it). If she sticks the middle finger, then my daughter can show the camera and she'll seriously get scared, because before the police warned her not to do this again or she could be charged. Even if she doesn't do it and notices daughter has a camera, then she certainly won't risk doing anything in the future. I think this is the best indirect way to stop this without getting her in trouble and it gives us satisfaction.