She just isn’t very well dressed. She’s wearing very functional looking waterproof snow boots. I can’t really think of anything that makes a broader proportion of women throw style to the wind and wear something highly functional than a snowy or rainy day.
On snow days they all wear those hideous functional boots.
People like to dress in different styles. The end.
The exact same thing that makes some teenage boys choose a ‘classy’ look over and ‘arsty’ one, and vice versa.
Those are the ones who want jobs.
She’s dressed appropriatly. It’s very hard to find.
I was thinking a skinned mattress myself.
Oh, and she’s in her teens. I am a noted prig and even I mildly…okay, I don’t actually care…wonder how old you are. 
I’m still hoping the OP will explain “arsty” to us. He’s from/in Ireland and almost all of the rest of us aren’t. Fashion is definitely a local phenomenon.
I think you’re thinking too deeply on this. It’s personal style, with the possibility that for individual girls, there might be specific factors contributing in, possibly parents that lean toward a more conservative look and if the parents control the girls’ clothing allowance, might reflect that.
I think “presentable” is purely subjective – unnatural hair colors are very on trend right now, more than ever this is seen as perfectly presentable, and will vary a lot depending on where you live, or what field you work in. It’s not nearly as counterculture as it was say, twenty years ago.
What you are calling classy, I would call more of a “classic” look. And again, it’s a style choice.
For girls who are interested in fashion, they might play around with a whole range of styles and looks, and dress differently for various events and occasions.
This is what I was going to come in and say. Is there something more to this question that I’m not getting? Is “artsy” (artsy?) a euphemism targeting women only?
Unlit and unless the OP gives pics of his/her daughters and friends vs the other schoolgirls being compared too (Or reasonable facsimilies) … I have no idea what the OP means by ‘classy’ vs ‘artsy’.
Same.
I dressed like my peer group dressed. Still do, I guess.