Actually, if she can’t demonstrate she had the idea first or at the same time, it is theft of intellectual property. If he sent in a prospectus for the book and she copied it, she owes money.
unfortunately the person suing posted on face book the proposal...at that point it is fair game for any writer to steal the idea. if the author can prove that Chelsea had special access to the idea then there might be a law suit. but the moment the person proposed in an open forum like face book they took away the few protections they had on there idea for a book.....that is why before publishing most authors are carful about who has access to there drafts and if they are published a lot of times will have you sign something if you are a beta reader.