Hmm, the top and cami (or are those straps a sports bra?) put emphasis on the width of her shoulders. I can see why the other mc is a little uncertain when she has such an androgynous style, and even when wearing more fem clothes pushes what are generally considered masc traits like her broad shoulders.
Edit: Actually looking at it closely, she doesn't even have broad shoulders, the outfit is just so good at emphasizing them that I made a mistake.