Yep, its as simple as the writer understanding that no one worries about super OP characters and creating a bunch of side characters to be concerned for. The main character is just a fun plot device the world centers around.
Humor aside, turning into a tree would be an interesting stress response for a magical species. Something killing your kin? Turn into a tree and wait it out until the source of stress is gone.
Its a dark story but I hope the priestess makes it out. She has some legendary tier mental fortitude to put on on an act after all she has been through.