Well, one possible consequence could be that Bella starts to transform more quickly into a vampire. Since James is a powerful and rather cruel vampire, his bite might carry some extra 'oomph' that accelerates the process. She might also have more intense visions or nightmares during the transformation due to the nature of James.
One interesting plot could be Bella's struggle to control her new vampire powers. She might face difficulties in adjusting to her heightened senses, like being overwhelmed by the smell of blood. Another plot could involve her relationship with Edward. Since she's now a vampire, their dynamic might change, and they could face new challenges together.
Bella's character often becomes more confident. As a vampire, she has newfound strength and abilities that make her less timid. For example, she may be more assertive in her relationships and in dealing with threats.
The plot changes drastically. For starters, the Cullens might have to deal with the fact that Bella is now bitten by a rogue vampire. They may face some internal conflict about whether to help her or not. Edward's character would be deeply affected as his love for Bella is put to the ultimate test. He has to decide if he can still be with her now that she's been bitten by his enemy.
It could be a rogue vampire. Maybe a vampire who has a grudge against the Cullens and figures that taking Bella is the best way to get back at them. This vampire might be acting alone, thinking that he or she can use Bella to bargain with the Cullens for something they have.
In some of these fanfictions, one plot could be that Bella's kidnapping is part of a scheme by a new vampire coven that wants to use her as bait to lure Edward. They might think that by having Bella, they can draw out Edward and his family and then overpower them to take over their territory.
In some fanfictions, Bella might get hurt during a fight with a rogue vampire. For example, she could be caught off - guard while trying to protect someone in Forks. Another scenario could be when she is exploring the woods alone and stumbles upon a dangerous supernatural creature that attacks her.
One challenge could be the acceptance from the two different communities, the werewolves and the vampires. Another might be the safety of Bella during the pregnancy, as it could attract unwanted attention. And of course, there's the relationship between Paul and Bella, which may face strain due to the sudden change in their situation.
Well, often the story develops with Bella having to deal with the new reality. She may face rejection from some in the vampire world who were part of her life before. The pregnancy could be a difficult one, with possible threats to her life. Paul would be constantly by her side, trying to find ways to keep her safe. And there could be a power struggle within the werewolf pack regarding this unexpected situation.
A lot of these fanfics deal with how the Cullen family adapts to Bella's pregnancy. Some may show them being protective, while others might show internal conflicts within the family about what this means for their future. It also often includes themes of motherhood, like Bella's thoughts on being a mother and what kind of mother she wants to be.