I didn't know about this series, so I checked the tags of the manga, let's see: "abuse", "depressing as fuck" "violence", etc... Ah ok... I'll give it a lecture anyway
^ I wonder the same, maybe that's how it was in All Stars? Because of the change of uniform? Maybe they are waiting for an important scene between them? I think in All Stars she did wear it, idk, I hope they add her hairpin soon...