@blue not it's a girl and making her a boy is actually an error of the translators. I didn't read the begining in english so i don't know if they translated this but in the early chapters we can see that her father wrote something like ''infidèle daughter'' (i don't know how to say infidèle in english). This was when they first ran to get the invitation the palace. Then on the first meeting with Luke, Rosalite didn't hide her with the boys cause she's a girl. She even said that she was a little worried but if Luke came to be interested in her she'll just have to remove her shirt, meaning she's a girl. And last but not least in the chapter where rosalite had period cramps, Aster said to Rion than she experienced it too, which is the most obvious évidence that Aster is indeed a girl.