She was not meant to have killed him, just injured him enough to escape.
After the Orcs and Bannor warred for some years after the arrival of the Bannor. Orthus was their war-leader, effectively leading the male orcs. The Bannor were pushed back, but regrouped, and began defeating the clan armies. There are two camps among the orcs politically, one that wants to continue a frontal war, another that sees that as suicide. Orthus and a large group of orcs leave, becoming the barbarians and ravaging other lands such as the scattered outposts of the Kuriotates or elves, and fight with the frostlings probably, but Mulcarn by now is quite distracted by Kylorin's rise among the Amurites.
The rest of the Clans cease their full war with the Bannor, but continue guerilla attacks. Rantine is tired of seeing killing and dying and tries to broker peace with the Bannor. They agree, but wipe out several villages nearby after, just to be safe. (They are used to dealing with backstabbing demons, but still, it isan honorless thing to do.) Jonas threatens Rantine, who retreats east for a few years, until called back by Bhall.
Meanwhile the clans are split again over those who accept peace and those who want to carry on their attacks, and over leadership as well. All the tribes acknowledge the priestesses, but not a war leader, until the events of Jonas story.
That's how it works in my mind, anyway.