Her True Intention
A minute before Long and Lesse charged to save Elric from the cursed blade, Kahayag was also in contact with the Envoy via astral communication.
Kahayag was not just a fine warrior but a smart one as well. She knew pretty much the weakness of the cursed knife and seeing that the two dragons are about to push for a breakthrough, she also realized the possible move that they can grab.
She knew that the Tribulation of Light contains the power of heaven and its purifying attribute as well. Basically speaking, if the two eastern Dragons are not dumb, they could grab that opportunity to channel the lightning from the Tribulation and dispel the soul locking curse that had been holding Elric back.