Neither is pretending to be sick and fake sneezing when someone is trying to clean up their immediate area. Or mocking a person on the low or judging the responses of others to a particular stimuli, simply because it isn't your own. Talk about things that aren't good for your karma.
Nothing is private on a plane. If you have your phone open and someone reads or views your screen, that is on you. You have zero expectation of privacy when you are shoulder to shoulder (and practically butt to belly button). That would be on them for being trashy, albeit quietly trashy.
I agree she shouldn't make any response to "those" people, because none is required. Do you girl.