Hikari is a crappy character. She was full of herself because she was the only developed omega out the two. And because she was the only developed one she experienced hardships though it doesn’t justify the actions.
As for the comment on her body I believe that she mentioned that it’s abnormal how quickly is maturing. However, in this realm it seems that it’s kind of unique among her family. I have to reread from the beginning but omegas from that family are superior and it may go beyond just producing alphas. Or maybe it’s something about her body. IDK. I don’t hate her, but a redemption arc would be nice and I’m looking forward to her finding peace and treating her brother better.