Ember is the problem. This is probably the most absurd character I've ever seen in a games. Due to the fact that not everyone has probably finished the game, I will write it in a spoiler.
In this particular case Owlcat has kept to canon, though.
Nocticula ascends if you close the worldwound. That is the deciding factor, not Ember. She already likely is chaotic neutral by the time you meet her in the demonic city, which is why she can see the Hand of the Inheritor. His invisibility spell protects him from the sight of evil creatures. You can actually ask her about it.
If you fail to close the worldwound, again regardless of Ember, Nocticula won't ascend.
