Maybe the story could be about Bella exploring other ways to deal with the vampire world without becoming a vampire herself. For example, she might focus on using her knowledge to protect humans from vampire threats.
Bella would definitely be one of the main characters since the whole concept revolves around her not taking the bite. Edward would also likely be a main character as his relationship with Bella is central to the 'Twilight' series which this fanfiction is based on.
One possible plot could be that Bella's malnourishment is due to a difficult situation at home. Maybe her family is poor and can't afford enough food. Her friends in the fanfiction world then notice her frail state and start to help her by bringing her food and getting her proper medical attention.
Well, perhaps Harry discovers Snape's dog has bitten someone. He might initially be reluctant to get involved but his sense of justice makes him step up. He could start by finding out how severe the bite is and then look for a way to clean the wound properly to prevent infection.
In this fanfiction, perhaps the dog that bit Snape was under some dark magic influence. Harry not only cleans the physical bite but also has to figure out the source of the dark magic. He might have to search for clues in Hogwarts, and along the way, he and Snape start to understand each other better.
Perhaps the fanfiction could focus on how Bella adjusts to the werewolf lifestyle. Since she was previously involved with vampires, her new married life with Jacob could be full of cultural and lifestyle differences. For example, she might have to get used to the pack's traditions and the way they interact with the forest around them.
Perhaps it's a more romantic take. Bella could be locked in a room by a love interest who is too shy or conflicted to face her directly. So, in a rather clumsy way, they lock her in a room with the intention of finally confessing their feelings but are struggling to find the right words.
Well, it could be about Bella and Liam going on adventures together. Maybe they face some challenges in their relationship, like dealing with jealousy from other characters. And they might also have some really sweet moments, like sharing secrets under the moonlight.
In the fanfiction, Bella might be having surgery due to an accident. She was in a car crash or some other mishap. The story could focus on her recovery process after the surgery. How she has to relearn to do simple things, and how her relationships with the people around her change as they help her through this difficult time.
Well, perhaps Bella starts learning self - defense skills. She could train with a mysterious mentor and then be able to take on any threats in her world. For example, she might face off against some dangerous supernatural beings and defeat them with her newfound badassery.
Maybe Bella Swan discovers Cortez's work and it changes her perspective on something. For example, if Cortez is an artist, his art could inspire Bella in her own life in Forks.