When I hear or read theories about Bella being an anti-feminist character, those theories are usually predicated on her choices. In the beginning, she chooses romantic love over everything else. Eventually, she chooses to marry at an early age and then chooses to keep an unexpected and dangerous baby. I never meant for her fictional choices to be a model for anyone else's real life choices. She is a character in a story, nothing more or less. On top of that, this is not even realistic fiction, it's a fantasy with vampires and werewolves, so no one could ever make her exact choices. Bella chooses things differently than how I would do it if I were in her shoes, because she is a very different type of person than I am. Also, she's in a situation that none of us has ever been in, because she lives in a fantasy world. But do her choices make her a negative example of empowerment? For myself personally, I don't think so.
In my own opinion (key word), the foundation of feminism is this: being able to choose. The core of anti-feminism is, conversely, telling a woman she can't do something solely because she's a woman—taking any choice away from her specifically because of her gender. "You can't be an astronaut, because you're a woman. You can't be president because you're a woman. You can't run a company because you're a woman." All of those oppressive "can't"s.
One of the weird things about modern feminism is that some feminists seem to be putting their own limits on women's choices. That feels backward to me. It's as if you can't choose a family on your own terms and still be considered a strong woman. How is that empowering? Are there rules about if, when, and how we love or marry and if, when, and how we have kids? Are there jobs we can and can't have in order to be a "real" feminist? To me, those limitations seem anti-feminist in basic principle.
Do I think eighteen is a good age at which to get married? Personally—as in, for the person I was at eighteen—no. However, Bella is constrained by fantastic circumstances that I never had to deal with. The person she loves is physically seventeen, and he's not going to change. If she and he are going to be on a healthy relationship footing, she can't age too far beyond him. Also, marriage is really an insignificant commitment compared to giving up your mortality, so it's funny to me that some people are hung up on one and not the other. Is eighteen too young to give up your mortality? For me, any age is too young for that. For Bella, it was what she really wanted for her life, and it wasn't a phase she was going to grow out of. So I don't have issues with her choice. She's a strong person who goes after what she wants with persistence and determination.
