People get caught up on the 'feminism'
It seems like there is a lot of debate over how Jennifer's Body can have have a feminist message if the titular character is so antagonistic and sexual allure is so present.
I don't think that the ultimate theme of the film is feminine empowerment. It is a feminist film because it was made by females, for females (despite how it was marketed), about female issues. Feminism in this case, is about getting the female perspective heard.
So it's feminist as far as context, but in the film itself there's something much more subtle and layered going on. It's really about growing up, about a friendship falling apart, and a shy, kind-hearted person learning to stand up for herself. Diablo Cody is a good writer in part because she's unafraid to show the ugliest sides of her characters, and I think it makes the movie even more feminist in a way because she refuses to prettify the female population and instead draws them as diverse, imperfect, human individuals.
People also seem to think that the fact that women are the ones doing the killing and saving in the film is supposed to carry an empowerment message. I disagree. I think this film is just like great tragedies-- it reveals dark tendencies in human nature/society in the hopes that we can learn from them and live more peacefully.
Also interesting: I found an interview of Ms. Cody where the interviewer asks her why she decided to subvert the horror convention and put women in control. Her answer was, "Because it's realistic." The interviewer laughed like it was a joke, but Cody looked absolutely serious, and I believe her. It wasn't a choice made specifically to subvert the genre. It was a choice made to reveal something very true and very important about adolescent relationships.