A dear friend of ours is a big fan of the Death Note series - a Japanese manga/anime/live action series about a notebook. If you write someone's name in the notebook while concentrating on their face, they will die of a heart attack in 40 seconds. This notebook falls into the hands of an idealistic law student who starts killing off all of the bad guys he can find.
The police go after this mystery vigilante with the aid of a mystery vigilante hunter. The vigilante hunter is later revealed to be a young man with a sweet tooth, a shaggy haircut and an emo fashion sense. In some respects, he resembles the Death Note killer. In other respects, they are both the kind of cute manga boy that pre-teen to teenaged girl fans love.
Yes, I'm afraid our friend the Death Note fan is a preteen girl. In general, we're fine with that. Our tastes are pretty adolescent at best. In this case, however, we're going to have to say that we don't get the appeal. The film is pretty well done, with some interesting philosophical points (who would you kill?), funny quirks (the apple-eating death-demon who can only be seen by those who have handled the notebook) and clever uses of the premise. But on a gut level, we didn't get it.
In conclusion, it could have been Twilight that she's into.