Unfortunately, if Rowling were to ignore any book that comes along like that, then she loses her right to enforce her copyrights. Copyright would mean nothing if it couldn't be enforced. Being litigious is the only choice at this point to enforce her copyright since RDR couldn't be convinced to scrap publication of the book. Unfortunately, letting this book sink on its own merits is not the way the world works. The situation here hasn't played nice at all when the original author has rights to stop it.