Here (Australia) the vast majority of high schools have mandatory uniforms, both in the private and public spheres.
The conservativeness of those uniforms, and the way in which they are worn varies greatly, but that's the 'normal' approach here.
My eldest daughter attends a public school which does NOT have uniforms, and that's an oft-remarked on facet of the school, due to it being unusual.
It's been great, to be honest. She's much more comfortable and confident wearing her own clothes, and somehow the school has managed to avoid the whole thing turning into a fashion show, which is a good achievement.
I know there is a dress code, but it's not aimed at some of the usual suspects (for example, if you want bright green hair, that's fine). Instead, it's targeted at brand labelling. The entire ethos of the school is to encourage individuality (for better or worse...lol) and the intent of the dress code is to protect individuals from peer pressure.
Take teens and jam them into school environments, and of course there will be peer pressure. At my high school (which had pretty strict uniforms) there was a subtle art to signaling you weren't uncool, or whatever. Changing from black school shoes to runners at lunch time, never quite managing to button up the top button of the shirt, or really tighten your tie...obviously never wearing a tie on the way to school or the way home. The brand of runners you wore at lunchtime was a big one. For girls there was a strange pressure around wearing skirts short, and socks very thick but scrunched down.
In any case, my point is that kids will be kids. Whatever policies or dress codes...or absensce of dress codes...we use, there will be issues around dress. The best we can do is treat them in an adult fashion, explain why the dress code is in place as it pertains to them (which a LOT of dress codes fail entirely to do), and try to foster a culture of inclusiveness.
In terms of the OP, that girl has every right to be upset, I believe.
