The Whispering Trees (The Thickety #2) by J.A. White

After Kara Westfall’s village turns on her for practicing witchcraft, she and her brother, Taff, flee to the one place they know they won’t be followed: the Thickety. Only this time the Forest Demon, Sordyr, is intent on keeping them there. Sordyr is not the Thickety’s only danger: unknown magic lurks behind every twist and shadow of the path. And then Kara and Taff discover Mary Kettle, an infamous witch with an unspeakable past—she is everything their village fears about magic.

When Mary shows them the path leading out of the Thickety guarded by Imogen, a creature more monster than human, Kara is hesitant to trust her. But then she offers to help Kara learn to cast magic without a grimoire…and this could be Kara and Taff's only chance to escape.

Or the first step down a dark and wicked path.