Good Girls Stay Quiet, Paperback/Jo Cassidy

There's safety in silence... Fifteen-year-old Cora Snow has a secret only her "Daddy" and her journal know about. Aside from Daddy, the only people Cora talks to are her teachers and imaginary friends. She obeys all of Daddy's commands, like calling him "Daddy," to keep him happy, and herself alive. Besides, it's the only normal she's ever known. She's content in her bubble until one day her journal goes missing at school. In order to keep her secret, Cora is forced to befriend the students most likely behind the theft. Since she's never been friends with humans before, it makes acting naturally with them that much harder. Soon, threats appear--blackmailing things like test answers and money in exchange for the journal. Cora has to break all the rules she's lived to keep her and Daddy's secret safe. His stormy moods add to the difficulty of meeting the blackmailer's demands, often getting her sent to timeout, aka a locked basement. If Cora can't track down the blackmailer and destroy the journal, Daddy will get sent to jail, and if he has time, send Cora six feet under.