Well, one reason could be a new start. Maybe she wants to break free from her old self. In some fanfictions, she might cut her hair after a big event like a break - up or a change in her life situation. It could also be a symbol of her growing independence, showing that she's not the same girl she used to be.
One reason could be for a disguise. Maybe she's on the run from some bad guys in the fanfiction world and changing her hair color helps her blend in better.
One possible plot could be Bella struggling to hide her discomfort during her period while dealing with the usual vampire - human drama in Forks. Maybe she's worried about Edward smelling the blood and it adding an extra layer of tension to their relationship.
In fanfiction, Bella might be the Volturi's princess because of a misinterpreted prophecy. The Volturi could believe that Bella is the key to something great, like ruling over all vampires or finding a way to live in the open without fear. So, they give her this princess - like status. Also, it could be due to her relationship with Edward. If the Volturi see Edward as a threat or an asset, they might use Bella to manipulate him, and making her a princess is part of that strategy.
With her friends, they might be really surprised. Some friends could be supportive and think it's a great new look for her. But others might be a bit critical, which could cause some strain in those relationships. For example, if a friend was used to her long - haired, more traditional look, they might not like the sudden change.
A woman might cut her long hair due to a major life event or transition. For example, Sophia cut her hair as a symbol of the big changes she was going through in her life. Also, it could be influenced by fashion trends. Sometimes when new short - hair trends emerge, women with long hair might be tempted to cut their hair to be in style.
Perhaps she is deceived. In some fanfictions, she could be tricked into believing that the Volturi are the 'good guys' or that they can offer her something that the Cullens can't. It could be a false promise of safety or a way to protect her loved ones that leads her to become a Volturi member.
One reason could be to explore a different side of Bella Swan. Writers might want to break away from the typical good - girl image of her and see how she would function as a more villainous character. It adds a new dimension to the story.
One possible reason could be a symbol of a new beginning. Maybe she's had a major life change, like starting a new chapter in her relationship or in her studies at Hogwarts. It could also be a sign of rebellion against the traditional image others have of her. In some fanfictions, she might cut her hair to fit in with a different group or to show that she's breaking free from her old self.
Well, it's simply immoral. Incest is not acceptable in society, and fanfiction, while being creative, should also adhere to basic moral principles.
One reason could be the allure of the vampire - human relationship in both the Twilight and Vampire Chronicles universes. Writers might want to combine the two to see how Bella's experience with vampires like Edward in Twilight could translate to a relationship with Lestat.