Perhaps a new character could be introduced as the hero. A wizard or a powerful human with some extraordinary skills. This new character could be someone who has been observing Peter's actions from afar and decides to step in to save Bella when the time is right.
Alice could be a crucial hero. Her ability to see the future could help in planning the rescue. She could foresee any traps or ambushes set by Aro and guide the others to avoid them. Also, her friendship with Bella would make her determined to save her from Aro's clutches.
In some 'Peter kidnaps Bella fanfiction', it could be that Peter is actually in love with Bella but in a very twisted way. So he kidnaps her to have her all to himself. Bella initially hates him but as time passes, she starts to understand his troubled past that led him to this extreme behavior.
It could be that the real antagonist is the situation or the world they live in. For example, if they are in a post - apocalyptic world where resources are scarce, Paul might kidnap Bella to ensure his own survival or the survival of his group. In this case, the harsh environment is the main driving force behind the antagonistic act.
Well, apart from Bella, there could be a male lead who is the creative director of the 'for him' brand. He could be a strict and demanding professional but also has a soft side. Then there are the makeup artists and hair stylists who are always around Bella during shoots. Also, there could be Bella's agent who is constantly trying to get her the best deals and manage her career. There might be some models from other agencies who are jealous of Bella's rise in the 'for him' modeling world.
There is also a possibility that a lone vampire, who has a sense of justice or who has been secretly observing Bella and has grown fond of her, decides to take on the Volturi and rescue her. This vampire could have some special abilities or knowledge that gives them an edge against the powerful Volturi.
She might try to escape. Bella could use her wits and any skills she has to find a way out of the situation.
It could be a rogue vampire who wants Bella for her unique blood. There are many vampires in the Twilight world who might be tempted by her smell. Another potential kidnapper could be a vengeful werewolf who blames Bella for something, perhaps for the way the vampires and werewolves' relationship has changed. It might also be a human who has somehow found out about the vampire world and thinks they can use Bella to gain power or knowledge.
There could be a dark spirit that haunts the woods. It's jealous of Bella's presence and tries to drive her out. Another antagonist could be a neighboring landowner who wants to expand their property into the woods where Bella lives.
Another potential helper could be a group of volunteers. There are often volunteer organizations that focus on helping the homeless or pregnant women. These volunteers could provide Bella with things like warm clothes, food, and even help her find a more permanent place to live. They might also offer to accompany her to doctor's appointments for her pregnancy.
She could interact with Elena. Since Elena is a central character in Mystic Falls, their paths are likely to cross. They might start as friends or rivals, depending on the story.