During the battle Edith didn't sit still, she knew that there wasn't much she could do in terms of helping Lirian, so she slowly retreated behind the cover of a tree that was closer to the river and hide there.
She knew that it was only a matter of time before the group reneged on their promise, and it wouldn't be difficult for them to throw a spear her way while Lirian was distracted, if such a thing happened she knew that she needed to find cover and right after that Lirian would use storm caller.
It was mainly because of the storm caller ability that she hid as she was uncertain as to how much Lirian would be able to control its destructive power, if he wasn't able to handle it properly she knew that he'd hesitate to use it out of fear of harming her.
The tree was the perfect spot for her to hide because she could use it as cover, and if the power of storm caller was too much she'd be able to escape in the river and get washed up down the river.
