I have a feeling that deliberately covering up the DOT sticker or taking it off for no real reason could get you pulled over and questioned. He turned around to follow her for a reason though, whether or not it was the helmet. Cops don't just spin around in the road like that for nothing. She changed how she was riding or something when he was behind her, because he waited for a while to pull her over. Then, in the end, she was ticketed for the helmet. But the fact remains, he picked her out going the opposite way for a reason. The ticket for the helmet is just what she ended up with. You can fight that one though. She needs to think closely on what would have gotten his attention in the 1st place, if it wasn't the helmet. 
Oh my, but I beg to differ....I've had numerous cops, in different cities, whip right around in the middle of the street and chase me down because of the way I looked, backwards cap, long hair, goatee...stopped or going with the traffic flow... On several occasions, the very first thing the officer said to me, in front of my wife and two kids in car seats in the back, was "We can do this the easy way or you can go to jail right now". As much as you hear about "not profiling", everybody does it every day and it's easy to test if you don't believe. Put yer baseball cap on backwards and paint your car rat style, or ride a bob or chop and see if you don't get hassled two or three times as much as a guy wearing a $400 set of leathers on an new $20,000 sportbike doing the same stupid stuff on the road, or the guy in the Escalade, speeding, weaving in and out of traffic talking on his cell phone. Unfortunately, in my personal opinion, she got stopped because she fit the profile of radical teenager. And, while they say they don't have quotas for writing tickets, the more tickets you write, the better it looks on your next personnel evaluation, a girl is an an easy stop, most people pay the fine and he looks like gold to his superiors. The more you stand out from the crowd, the more likely you are to get noticed and when you get noticed, you are, as far as I can see in any aspect of life, evaluated on how you present yourself. Nice clothes, shiny car, well groomed (white) = successful, intelligent, respectable, and as those attributes lessen, so does your standing in whatever community, to then point where primered car/rat bike, raggedy jeans and sneakers, long/punk hair (black) = un-educated, welfare, druggies, out of control, slackers, trouble makers, generally, not someone you want living next door. The more you fit this end of the profile, the more likely you are to have already been thru "the system" and therefore receive more intense scrutiny and actual harassment.Truly race is more of a "color gradient" issue, but ask any non-white folks if this isn't true, and they'll also tell you that no matter how nice your clothes are, if you can't change your color to white, you're still gonna get hassled even within your own race, "If you're light you're alright, if you're black, better git on back". This is class/race "warfare" on the economic front, the more you look like you're at an economic disadvantage, or outside the "norms" of society, the more likely you are to become even more economically/socially challenged. Cops are there to uphold the "norms" of society, the only thing she (or any of us) can do to avoid it, is to not attract attention by, in this case, A: riding a motorcycle, and B: expressing her freedom of speech. Doesn't matter what you're speaking out for or against, when you speak out, expect to be challenged, freedom has it's price.
Or, maybe he thought she was hot and wanted to hit on her. Some cops do that....
