Now that I think of it - her halo kinda looks like a crown.
It does to me too. Moreover it also looks like one of those icons you might see in a game floating on a boss enemy (or their health bar) to indicate they're the boss.
Yeah, it does, doesn't it? It certainly would fit on top of a boss enemy. Honestly, this is an interesting concept that they can't see what halos even look like and only sensei could.