Bella could develop morally. Initially, she might be hesitant to take extreme measures against the supernatural threats. But as she witnesses the harm they can cause, she becomes more resolute in fighting them, even if it means making tough choices. This development could also be influenced by the experiences and values of Sam and Dean that she absorbs over time.
Her character could develop in terms of her relationships. Maybe at first she has a bit of a strained relationship with Dean because he's overprotective. But over time, they grow closer as she proves herself. She could also form a strong bond with Sam due to their shared interests in research.
It could be demons. Demons are often the main antagonists in the Supernatural universe, and they might target Bella because she is related to the Winchesters. They could try to use her as a bargaining chip or a way to get to the brothers.
Yes, there might be. The 'Supernatural' world of Sam and Dean and the 'Harry Potter' universe are both very popular, and fanfiction often likes to cross over different fandoms in creative ways. Some fans might have come up with the idea of making Harry Potter be related to Sam and Dean as their sister in a fan - created story.
In some fanfics, there could be a plotline centered around Bella's love life in the context of being Dean and Sam's sister. Maybe she falls for another hunter, and the brothers have to approve or disapprove. There could also be a plot where Bella is haunted by a past event that only she remembers, and she has to rely on her brothers to help her figure out what really happened and how to move on.
One idea could be that Bella discovers she has special powers because of her relation to Sam and Dean. Maybe she can communicate with spirits in a unique way that helps them on their hunts.
Bella's character might become more confident. Knowing she has a powerful brother like Aro could give her a sense of security. She may also become more assertive in vampire society.
Sam might become more assertive in his beliefs. When they go back in time, he could encounter situations where his modern - day knowledge about certain supernatural entities clashes with the beliefs of the past hunters. Instead of being swayed, he would stand his ground and try to convince others. As for Dean, he could become more empathetic. In the past, he might meet versions of his family or friends in difficult situations that he didn't fully understand before. This would make him more understanding and kinder towards others in similar situations in the present.
Bella could interact with Sam and Dean in a very interesting way. Given her own experiences with the supernatural in the Twilight world, she would have some knowledge to bring to the table. She might be a bit of a nuisance to them at first, like constantly asking questions and fangirling a bit. But then, as she proves herself useful, like by using her knowledge of Twilight vampires to help them with a similar - type of supernatural being they encounter. Sam would likely be more patient with her, while Dean might be a bit gruff but would eventually warm up to her.
There's a fanfic called 'Sister's Bond'. In this story, the sister is brought into their lives in a rather mysterious way. It shows how she struggles to adapt to the life of hunting monsters while also trying to understand her new - found brothers. It's full of action and some really heartfelt moments between the siblings.
In a fanfiction, their sister could be a prophet. She starts having visions that lead the boys to new cases. But there are forces that want to use her for their own gain. Sam and Dean would have to fight not only the regular demons and ghosts but also those who are after their sister.
The relationship can be developed through shared experiences. For example, if they go on a camping trip together, they can bond over building a tent, cooking over a campfire, and sharing stories under the stars. This would make their relationship stronger as they rely on each other in the wilderness.