1. The movie "Gravity" is primarily an action/special-effects pageant about an astronaut trying to get safely back to Earth after an accident destroys the space station she was on. The book "Gravity" is a medical techno-thriller about a doctor in space fighting a disease outbreak on a space station. Reasonable people can probably disagree about whether the movie, given its significantly different plot, is even a derivative of the book at this point.
2. The lawsuit was not regarding plagiarism, but rather for breach of contract related to the film rights for the book. Gerritsen alleges that Warner Brothers was bound by and failed to observe the terms of a contract she had signed with a company which became a subsidiary of New Line, which in turn became a subsidiary of Warner Brothers. The court found that even if all allegations in her complaint were taken to be true, they still would not establish that Warner Brothers was bound by that contract. This mostly seems to depend on the arcana of contract law and how mergers and acquisitions pass obligations on (or don't pass them on), and suggests that the main issue was either she or her attorney did not sufficiently understand those arcana (given that she apparently contracted for a percentage of net rather than gross, a lack of experience in what makes a good contract for film rights seems likely) in order to build a successful complaint.