Well, a great plot might be that in a human - dominated world, Bella and Edward are trying to keep their true identities secret. But then, there's a series of mysterious disappearances in the town that they suspect are related to the supernatural. So they start to investigate together. Also, perhaps there's a prophecy in the supernatural world that involves a wolf - vampire - human bond, and they are unknowingly part of it. And this could lead to all sorts of adventures and challenges for them.
A possible plot could be that Bella, being a wolf, has a unique connection to nature. In the human world, there's an environmental crisis that she senses. Edward, with his vampire abilities, helps her figure out the source which turns out to be a group of rogue vampires who are using the chaos for their own gain. As they work together to stop this, they also face the prejudices of the human society towards their 'abnormal' natures. Along the way, they might also discover new powers within themselves that are related to their wolf - vampire natures respectively.
One interesting fanfiction could be where Bella has to protect Edward from other vampires who see him as an easy target because he's human. It adds a new dynamic to their relationship as she uses her vampire abilities in unexpected ways.
A common plot is the exploration of their relationship in different settings. For instance, they might travel to a new place where vampire - human relationships are more accepted or more dangerous. This could lead to them facing new challenges together, like dealing with local vampire clans or human hunters who are aware of their presence. It also gives room for more character development as they adapt to new environments and situations.
Perhaps a plot where Edward and Bella decide to run away together from both the human and vampire worlds. They find a secluded place and try to build a life there. But they soon realize that they can't escape their natures completely. Edward still has his human vulnerabilities and Bella has her vampire instincts, which creates a lot of drama and conflict in their relationship.
One idea could be that they face unexpected challenges during the pregnancy, like financial difficulties. Maybe Edward has to take on extra jobs to support the family. Another could be that Bella's family is initially against the pregnancy because they think they are too young. And a third idea is that they discover they are having twins, which doubles the excitement and the stress.
One idea could be that Bella already has some latent vampire powers herself when she meets Edward. Maybe she can sense other vampires from a distance. This would add a new dynamic to their relationship as they both figure out what it means.
One plot idea could be Bella struggling to choose between her vampire life with Edward and her deep friendship with Jacob that has the potential to turn into more. Another could be Jacob trying to protect Bella from a new vampire threat while also dealing with his feelings for her. Maybe a plot where Bella discovers a new power as a vampire that Jacob has to come to terms with.
One interesting aspect could be how their relationship dynamics change. In the original, Edward was the vampire and Bella was the human, so reversing their roles might lead to a different power dynamic. For example, Bella as a vampire would have more physical strength and speed, which could make her more protective of Edward. Also, Edward as a human might struggle with his mortality compared to Bella's immortality, creating new tensions and storylines in the fanfiction.
A plot could be that Bella, as a vampire, has to pretend to be human around Alice's family. This would involve a lot of hiding her powers and dealing with the difficulties of being around humans all the time. Another idea is that Alice, as a human, discovers a way to make Bella more 'human - like' again, and they embark on a journey to find the ingredients or perform the rituals necessary.
One popular fanfiction could be about Bella using her vampire abilities to protect Edward from some new supernatural threat in Forks. Maybe she has to face a powerful vampire coven that has a vendetta against the Cullens, and in the process, her relationship with Edward deepens in new and unexpected ways.
One idea could be that Bella discovers she has a special power that only she can use to protect the wolf pack. For example, she might be able to communicate with the spirits of the forest which give her warnings about upcoming threats.