I do wonder where she could even find monsters that can deal with the founders.
The best she could do against Malik was stall him with the Strength Eaters. Behemoth - arguably her trump card - was also completely trivialized by Malik. Valravn at full strength is probably S-Class, but S-Class still means nothing against the founders, so Aglaecwif would be similarly stomped on as well.
Either Ella manages to summon an Apostle in some way to deal with the founders or one (or more) of the founders is working with her; I can't see many other solutions.
Has there been anything to indicate whether Nyx can mark regular joes or is it superhumans only? Wondering whether Xanthe could have one. He seems too important not to have a backup of
The way I see it, her resurrection power might be based on Memory. When she talks to "ghosts", it's just the residual echoes of the dead. When she resurrects someone, it's like loading a back-up save of the memories of the deceased (so I guess Ship of Theseus and all that).
Anyway, I'm leaning on yes. Ella used a monster related to Nyx's power to make sure Christie and Emily also resurrect if killed, so Nyx should have no problems using her mark on normal people as well.
On a related note, Ella gets pissed and kills the MC in the Bad End where he kills Christie, but Christie should have been fine given the resurrection mark. Did WeirdWorld just come up with the resurrection marks and so it's an inconsistency to be fixed, or does the MC absorbing someone's body actually override the resurrection?