In the Chrono timeline, Schala uses the last of her pendant's power to send your party to safety, meaning she and her mother get left behind. Queen Zeal then activates the Black Omen.
I assume in the original timeline, Schala used that power to rescue herself and her mother, meaning the queen didn't get the chance to activate the Black Omen.
(That's also my theory as to how the pendant eventually ended up in the Guardia dynasty's possession instead of lying at the bottom of the ocean; Schala lived out the rest of her days peacefully in the original timeline.)
This is just speculation on my part. I don't think there's anything in the game to confirm it, but as far as I know, there's nothing to contradict it either.
