Raine: Loosing someone dear to her again, her strider getting hurt/killed, grass fires and Zith slavers.
Nanithel: Showing her feelings to others, getting hurt emotionally, something bad happening to her family or animals, to be forced to stay in one place before she has travelled and found herself, dying.
Zuri: To always be alone, being to weak to defend herself, deep waters and not being able to run again.
That's what I have so far but you never now what kind of hidden fears my characters tries to keep secret:)