The Thickety #2: The Whispering Trees by J.A. White

This book is the second in the series, and you should begin with book one. Kara and her brother, Taff, are stuck in the Thickety, a forest of strange, dangerous creatures and trees, and Kara knows she must try to defeat Sordyr, the evil, magical ruler of the forest. Kara has lost her grimoire and believes she can no longer cast spells. A witch named Mary Kettle tells Kara that she's a special kind of witch and can make magic without the book. Kara has a unique connection with animals and slowly learns that she is able to control their minds. Mary helps the children survive the forest and helps Kara learn to develop her powers. However, Mary was once a vicious witch who killed and ate young children. She says she's changed, but can Kara and her brother trust her? Is it possible for Kara to defeat Sordyr before being killed by her new "friend"?

The plot is pretty straightforward with Kara learning to master her powers before facing the powerful force controlling the land. Mary's character adds an additional conflict to the quest, because it's never clear if she might be leading the children into traps. Taff is willing to trust her with his life, but Kara is leery to put her faith in the witch. The author continues this issue all the way into the climax of the story, so there were some surprising twists. The addition of Safi as a character will undoubtedly become a problem as the series moves along.