NObody should use spells above their level, unless they are specialising in something, or it's writteninto the plot. For instance, I think that when Mad-eye taught, he would have taught everyone the unfogivable spells etc, wouldn't he? So that means no first, second, or third years should no them. This should be in plot discssion...
Playing along with the plotline.
Divination is not perfect, its more of a suggestive thing, much like Mr. Potter's dreams.
I think we should also go on tradition that something will happen to the DADA teacher.
We should have main protagonist(s) perhaps Li, Dale, and Aerie
Main antagonist(s): Kai, Dani, and Sonia.
The group of antagonist should have a clear leaders, one that others fear, more of respect, much like a Draco. Their goal is to get rid of the gifted one, Li, because of her powers of divination. This is being supported by another figure, perhaps the head of the Slytherin because he/she is planning to blame the headmistress(?) of maybe stealing something.
And going along like the other Potter books, we need some kind of item. Important and powerful perhaps to all of Hogwarts and the wizard world. Hrmm... the Sorting Hat?
But the lost sorting hat was just a disguise, it wasn't actually stolen because of its power. But because the sorting hat witnessed a crime... I'll leave the crime to Phoe, 'cause I don't want to know, lol, I want to solve it too : )
No one will know the crime except for Phoe eh.
Li's vision is what is to happen, the three figures behind the dark one could be any of the three students, perhaps followers of the unknown figure, or enemies. The dark one could even be a student hrmm.... 😈