Another character that might show up often is Victoria. As an enemy in the original story, she could still be a threat in the fanfiction. Maybe she has new motives or strategies now that Bella is a vampire. And Rosalie, who had a complex relationship with Bella as a human, would probably be present to either help or cause some drama in Bella's new vampire existence.
Jacob could also be a common character. Even though Bella has become a vampire, her past connection with Jacob and the werewolf pack might still play a role. There could be some tension or new interactions between the vampires and the werewolves. And of course, Carlisle, as the head of the Cullen family, is likely to be in many of these stories to guide Bella in her new vampire life.
Edward is still very popular. Since he and Bella are now both vampires, their relationship takes on new aspects that fans like to explore. Another popular character is Alice. Her ability to see the future could be really interesting in a story where Bella is a vampire. She could foresee events that involve Bella and help her avoid danger or make important decisions.
Edward is almost always there. Since he's such a central figure in Bella's life as a human and vampire in the original story, he would likely play a big role in the fanfiction too. He might be the one guiding Bella through her new vampire life.
Her parents might be important characters. They could either be supportive of her career choice or initially be against it, thinking it's too difficult. Also, there could be a senior lawyer at the firm where she interns, who takes her under his or her wing and guides her through the complex world of law.
The Cullens are very likely to be involved. Edward, of course, would have a huge role as Bella's former love interest. Carlisle, with his knowledge and experience as a vampire, could help Bella adjust to her new life. Alice might use her precognitive abilities to foresee any problems Bella could face. Also, Jacob could be in the story. His reaction to Bella becoming a vampire would be interesting, considering his past relationship with her and his werewolf nature.
Edward would still be a very important character. Since he's Bella's love interest in the original 'Twilight' series, in the fanfiction, he would play a major role in Bella's new vampire life. He might help her adjust to her new powers and the vampire lifestyle.
Alice Cullen can be a very popular character. Since she can see the future, in a 'reborn as bella swan' scenario, her interactions with Bella could be really different. Maybe she tries to guide Bella in a new way based on her visions. Also, Carlisle Cullen is popular. His father - figure role towards Bella might be explored further in these fanfictions.
There could be a female character, Sofia, who is another member of the mafia. She sees Bella as a threat at first, thinking she'll steal her position or the attention of the men in the mafia. But as time goes on, they might form an unlikely alliance. There may also be a young and ambitious mafia underling named Antonio, who is always looking for ways to climb the ranks and his actions often impact Bella's situation in the story.
There could be Edward. Even if Bella is now immortal, Edward might still play a significant role. He could be either her eternal love or her adversary depending on how the fanfiction is written. Another character could be Alice. Since Alice has her own special abilities, she might be there to help Bella navigate the new world of immortality. For example, she could foresee some of the challenges that Bella will face. Also, Jacob might be a main character. His relationship with Bella, whether it's a friendship or something more complicated, could be further explored in the context of Bella's immortality.
There could be Edward. Maybe he is involved in Bella's life with her psychic powers. He might be curious about her abilities or even try to protect her from the consequences of using those powers.
There could be other vampires that Bella meets during her time as a vampire before the Volturi. For example, some lone vampires who are also trying to stay out of Volturi's radar. They could become her allies or foes depending on their motives.