Most of your post is aggressively stupid, wrong, and probably the result of mental defect or disease, but I will address part of it.
The reason is probably beyond your intellectual grasp, as would be any concept more advanced than finger-painting with your own feces, but here it is anyway.
She was resisting the lawful order of a police officer.
Most people, apart from you and, apparently, this teenage bitch-child, grow out of the “you aren’t the boss of me” stage in early childhood. Mature adults - that is, people who aren’t like you and have advanced beyond the toddler phase - recognize that we live in a society, and that other people also live in that society, and that the other people have decided that certain forms of actions are acceptable and others are not. We have codified those decisions into the form of “laws”. Those “laws” are binding on everybody - not just those who want to be bound by them, but everyone who lives in the society.
Unfortunately, there are people like this spoiled tantrum princess and you, who think that they get to decide if they get to live in the society and enjoy its benefits, but can decide on a case-by-case basis if they will obey the rules. (Obviously the case where the rules will apply is when it comes to other people, and not when it comes to the princesses.) Society won’t work if that happens - if people can get away with breaking or ignoring the rules by pitching a fit, things won’t go smoothly.
So we have appointed people to enforce the rules. We call those people “police”. These “police” go around looking for people who break the rules, and try to stop them. Of course the “police” do other things, but given your obvious mental limitations, I will try to dumb it down to your level.
Now one of those rules is that underage people may not possess alcohol. Obviously this is not one of the major rules. It isn’t like murder, or robbery, or crossing a rhesus monkey with a flatulent hyena and letting him post on the SDMB, as appears to have happened in your case, but it is a rule nonetheless. So the “police” ordered her to stop doing it.
Here’s a really, really advanced concept - if the police give you a lawful order, then in that situation he really is the boss of you. You do have to do it. You don’t get to say No or walk away or mouth off or spit on him or push him or anything like that. You have to do what he says, because he is speaking and acting as the representative of all the rest of us, who don’t give two toots on a tin trumpet about how fucking special you are.
So if you say No or walk away or mouth off or spit on him, he is authorized to arrest you. If you resist, he is authorized to use reasonable force to make you submit to the arrest.
And that is OK with the rest of us. That’s the point that you need to try to fit into the five hundred cubic centimeters of raw sewage atop your brain stem, if possible. Normal rational grown-ups are not like you. We understand the need for public order. And when some dim bulb bimbo complains that she got a smack in the sneezer when she refused a police order and spit on him and kicked him in the nuts, we don’t particularly care.
Now I realize that you don’t really understand the situation at all, and this is all recreational fapping and moral outrage because a story on the Internet triggered four of your available ten neurons, but look on this as an opportunity - you might be able to advance your understanding beyond that of a three-year-old enraged because grown-ups expect him to use the potty like a big boy.
You might not, too, but surprise us.
Regards,
Shodan