Lolly We know at some point one of the librarians says that Clem's house was on the never ever go there list. So Verna's testimony that they received books was entirely made up. I thought the McCullough sisters must have had a connection with Margery because they were all abused by their alcoholic fathers and hated them. They had that in common so Alice and the ladies probably didn't have to push too hard to have Verna cooperate. And they took care of her afterwards, so perhaps some promises were made?
This answer contains spoilers… (view spoiler)[The sheriff believed that Margery was guilty because she must have used the book Little Women to kill him with, as in bringing the book, and using what she had to kill him. The daughter’s testimony said that her father left the house, in terrible weather, WITH the book LW to return to Margery, therefore proving dad was out already with book, and the conditions were really bad, and that he and Margery had a good enough relationship he was eager to return the book quickly. Does that help? (hide spoiler)]