i'm not entirely sure either because i am stupid but here's what i think it is: she doesn't want to be seen as a "girl" because of objectification, even if being a girl is inevitably part of her identity, i think she feels she cannot escape the label of being a girl in the eyes of a male. as for the boy's uniform she wore it for akira's sake and stopped wearing it when she realized she does everything for validation from akira, but then she started wearing it again after she felt uncomfortable from the compliments about her. maybe i'm just dumb but i personally think the author could have explained this part a little more clear
why did she decide to stop wear the boys uniform? and why does she not like being seen as a girl, is it because of objectification?