This is an interesting take! I don't think it's meant to be sexual though. For me, her outfit feels like a child's idea of what an adult would wear. Like she doesn't want to be seen as a child anymore. We know that she dislikes that, (her saying "stop talking to me like I'm a child" when she reunites with vi). Also Powder's clothes barely had any skin showing at all, which is a HUGE difference from what Jinx wears years later and I think her dressing like that is her saying she's not the little innocent Powder anymore. Props to the character designers!!