If i'm not entirely remembering it wrong, she's considered royalty in some hereto unmentioned nation. And she would be considered the legitimate ruler at this time, because she was the daughter of the former or something similar, but noone knew of her existence before they killed him and found mentions of her in a diary, and at that time she was abroad with her guardian. Proof being her silver-colored aura or what you call it, being the exclusive of one of the two families she hailed from (one being royal family in country A and another being atleast famous in country B).
Her name at that time was Princess Marguerite, but she had no desire in trying to claim the throne that she by virtue of her birth had a very strong claim on. But when she and Ignis have another child ?
Her children also have pretty strong claims on the throne .
So basically, you're somewhat right. She could become a queen (doesn't want to) but instead of being a demon, she has partial beastman heritage I think (at most quarter or half)