Lol you certainly can't say more than nothing. Why didn't they do it? They didn't do it because they didn't do it... brilliant.
1. I am not in their mind, therefore it should be easy to understand that it is impossible to say anything more than this.
2. Are you sure this is a relevant question? Why is Elric's hair gray and not blue? This is the same type of question you're asking. Adelin *could* be a Sorceress, but is not. Now, you're asking this as if she *should* be a sorceress, but nothing says that she should... Hence my remarks about "requirement". Meeting a requirement is in no way an indication of anything.
It seems to me as you both are falling to the fallacy of Affirming the consequent
A Implies B does not mean that B implies A
Being a Sorceress implies being female and a magic user
Being female and a magic user does not imply being a sorceress.
You're stuck on the "but... she is female and a magic user, why is she not a sorceress?" question, but why? There is no reason to ask this question really. Humans have legs, does that mean that if something has legs it is a human? There is nothing that implies she has to be a sorceress, but you are insisting on she having to be a sorceress.