I don't buy the conclusion (spoiler)

By [I]spoiler[/I] I mean if you haven't read the book, you might want to skip this post.

My problem is that as a [I]philosophical point[/I] I buy that Shannon shot herself, but I don't buy it as an imitation of a real human being with human motivations. Although, maybe some others who have read the book could [I]sell[/I] the idea to me.

I could picture a girl overeating and getting fat, starving herself to a skeleton, killing herself, cutting and self-mutilation on the arms and wrists, being a whore, getting pierced, smoking, doing drugs, all sorts of things to punish and disfigure herself. But I don't buy a girl blowing off her own jaw with a gun. Not only that, but supposedly she is doing it to be free of the burden of beauty, but once she is free from that burden, she doesn't go out and become a rocket scientist or something. Is there something that I missed?