I suspect that Aura invoked Himmel's death specifically to coerce Frieren into going HAM against her undead army. Figure, we know that demons basically only use language as a tool, right? Well, if invoking Himmel's death successfully coerces Frieren into going old-school on Aura's undead army, and if Frieren going even *a little* too HAM burns *a little* too much mana, that might be enough of an opening for Aura's scale to do it's thing.