This isn't about the nun's habits but back to the idea of school uniforms...
Many years ago I read an article in Glamour magazine entitled "I've got that Catholic girls' school look". She was saying that she'd go shopping with her friends for, say, a fancy dress for a party, try on lots of slinky and flirty numbers, and end up with a long tartan skirt and a velvet blazer... it was her default, her comfort zone. The idea appealed to me (although I've never worn a uniform in my life, apart from scrubs and a white coat). But I love the confidence and authority conferred by the blazer, the "third piece", even though it barely fits my actual life...
Much later, when we lived in South Africa, our first 2 girls attended a convent school and wore uniforms. Actually all schoolchildren at all schools wore uniforms. Most often involving a blazer. And I found that adult women rarely dressed that way; I think it felt infantilizing to them. Instead, they would dress up with coloured shoes to match a pretty dress, and bling to go along... stuff that a schoolgirl would never get away with. (I never got the memo. My default is the Glamour girl's default.)