Are you sitting in class all day watching her 'looking at the pretty dresses' or are you just assuming from a passing glance? How do you know what she does when she visits others' houses? Maybe she cries when it's time to take the dress off because that's what kids do, complain when they have to hand things back?
My daughter wears trousers and dresses. She wanted a floofy tiered skirt once, so I got it for her, but she said she couldn't get down the slide in it, or ride the bikes at nursery without it tangling, so she'd changed into leggings by the time I'd collected her. So for nursery and playtime, we avoid the dresses (though she has tunics and leggings.) They're a pain in the arse.
Personally I let her wear what she asks for. She sometimes wears Pokemon t-shirts from 'the boys section', she wears flowered tunics, she has a couple of tops handed down from her brother. She chooses, and that's what's important to me - her choice.
I think you're making a lot of judgements just because the kid isn't dolled up like a cupcake fairy. The girl herself may not want to wear these things. I didn't as a kid, I didn't wear skirts or dresses until adulthood, I simply did not want to.
It's only 'sad' if she's genuinely being aggressively forced to reject certain clothes because 'girliness' and femininity are 'bad' or 'weak' or something, then it's a whole bunch of damaging lessons being taught. It's also only 'sad' if the girl herself is 'sad'. Which you don't know.