Norn is a part of Rudeus's biological family, but she has got no part in the Rudeus+Sylphie+Roxy core family. It's not her business. Sure, you could say she was speaking for Sylphie, but how can you then say in the same paragraph that it's silly to assume Norn would act like an adult responsible for herself? She can speak on an adult's behalf but can't be considered responsible for herself, like an adult? How does that work? Her speech was nothing but the tirade of someone whose personal feelings and values were hurt, yet it doesn't really concern her personally. Yes, her outburst did help Sylphie to better understand Roxy's character, but I was feeling sorry for Roxy, who just needed to stand there and walk away in tears, until she was stopped by Sylphie, who actually understood what was going on.

It's honestly kind of strange how entitled Norn is acting all the time. Perhaps it's nothing but a psychological defense mechanism when she suffered through the years of hearing how mediocre she is, while her sister and brother were called geniuses. She could grow up to be a petty villainess, but at least she does have a great brother, so maybe that won't happen.