Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu! - Vol. 4 Ch. 26 - The Fire of Hope

[MangaDex]

 

[Keimichi]

“Just appeared in my head” well, would you look at that deus ex machina

 

[CelticMutt]

@Keimichi - It's not a deus ex when it's been foreshadowed. She's already been possessed by another entity once before, the knowledge clearly comes from that entity.

 

[Keimichi]

@celticMutt
Yes, but just because it is foreshadowed doesn’t mean the knowledge didn’t suddenly appear into her head at the convenient time to suddenly solve the problem at hand.

 

[mage_goo]

@Keimichi

just because it is foreshadowed doesn’t mean the knowledge didn’t suddenly appear into her head at the convenient time to suddenly solve the problem at hand.

I don't get what you're trying to say.
By nature of foreshadowing, things foreshadowed doesn't happen suddenly but rather naturally.
She has some deity residing inside her, so naturally said deity would know how a mere human spell works and naturally, said deity would also inform her of that to preserve the vessel said deity currently residing in.
It all makes sense in hindsight.

Now if that doesn't happens because the deity's a dick or something, that'd make it a diabolus ex machina instead.