I think the mother may be a branch family of a royalty instead of the main family. I don't think Nunnaly's mother is a princess instead a high ranking noble
like that she's an illegitimate child that was gonna be sold off to an old man for politics; also that the main child died and they want to keep it in the bloodline so they'll accept the illegitimate kid (the mom)
just our assumptions tho, a shame the novel isn't ahead.
she is a royalti, remember the quest that say the queen from other kingdom search of girl who has strong ice afinity? Well guess what? They search the remaining royal family. The proof is lunaly hair colour and the ML also know