The wheels turned in Zariah's head as she tried to come up with a solution, no matter how Zariah thought of it, no matter what choice she made at this moment, someone would have to be sacrificed.
If Zariah admitted to the flame poison, the merfolk would never believe she had not been the one to cast it, only a fellow Crimson Wolf could determine the flame poison had not been cast by Zariah's blood.
As for everyone else, the flame poison was the flame poison, they did not have the insight to distinguish which flame wolf had cast it exactly.
The Sea King would rage, the Ethereal Domain would be dragged into it by association, all cordial relations would crash and the impending war could no longer be prevented.
Kristen would be taken out of Nile's care and the merfolk would never reconcile themselves to the fact that Nile was the only one who could save Kristen... which ultimately meant, Kristen would die.
