It was one of my favorites as a young thing.
It was about two little girls who, on Halloween, go to pick blackberries. They get lost and they get kidnapped by a witch. The witch turns out to be really sweet and she thought the little girls were stealing her thornberries. They make a thornberry pie to bring to the Halloween party. They go to the party and one girl dresses as a spider and the other as a princess. Ring a bell with anyone?
Was it a picture book? Easy reader? Chapter book?
The Thorn Witch! that was one of my favorite books. i still have it! it had the BEST illustrations. so dreamy quaint.