For my girls, this was totally normal. They get their mind set on a certain style for comfort or whatever reason and there's no changing it.
I've asked other moms over the years and my, oh my, do you hit a nerve with some. They will claim if you give in on this, then what battle will you lose next? I walk away thinking that mother has huge control issues, as if it's a reflection on them. And guess what, those kids who grow up with that excessive level of control don't turn out to be confident individials. They turn out needing to make mom happy or doing drugs to escape the rigidness.
And I am here to tell you that my oldest daughter is truly one of the most giving, caring, smart, funny, successful, brightest and talented kids a parent could ever dream of having. And she wanted to wear her pretty white slip everywhere when she was 5. In the winter I insisted she wear leggings and long sleeves underneath. Do people even buy slips anymore?
So, I firmly believe that a girls desire to pick and choose her own clothes out young is fine by me. Just keep them clean.
We too have received amazing, expensive clothes from nice department stores, or Gymboree, or hand me downs from cousins and my girls only liked certain clothing items. All my kids are very tactile dressers, meaning they want the clothes to be soft against their skin.
As they say, choose your battles, and i know for a fact that when I see a perfectly dressed kid at school, that mom did it.