it's cold outside

This morning there was snow on the floor. And ice. And it was proper cold. The little one went to school in his hat and a thick coat and a scarf and big gloves and wellies. The big one, however, went to school in a short sleeve shirt and a thin blazer. She WILL NOT wear a coat. Ever. Whatever threats I make. She seems to think it's not cool to wear one. If she had her way she'd go to school in a vest and hotpants. Where does she get these stupid ideas?