The Grace of Wild Things by Heather Fawcett

An inventive and fantastical reimagining of Anne of Green Gables—with magic and witches!—that explores found family, loss, and the power of a girl's imagination, from the acclaimed author of The Language of Ghosts and The School Between Winter and Fairyland. Perfect for readers who loved The Girl Who Drank the Moon and Serafina and the Black Cloak.
Grace has never been good at anything except magic—not that anyone believes her.
While other children are adopted from the orphanage, nobody wants Grace. So she decides to make a home for herself by running away and offering herself as an apprentice to the witch in the nearby woods. After all, who better to teach Grace to use her magic? Surely the witch can't be that bad.
But the witch is that bad—she steals souls for spells and gobbles up hearts. So Grace offers a deal: If she can learn all 100½ spells in the witch's grimoire, the witch will make Grace her apprentice. But if...