Westover says this about her roommate because the girl dresses in a way that is inappropriate for the Mormons Westover grew up with.
We can arrive at this answer because:
When Westover goes to college, her roommate dresses exactly that way, but the girl is a Mormon, which leaves Westover surprised, as the girl doesn't dress or behave the way she was taught.
This question is about the book "Educated" written by Westover.
You can get more information about Mormons at the link:
https://brainly.com/question/959938