She might be secretive. Since she's planning revenge, she can't let others know her true intentions easily. So she would keep her thoughts and plans to herself, only revealing bits and pieces when necessary. And she could be highly intelligent, devising elaborate plans to achieve her vengeful goals without getting caught.
She could be very determined. Once she sets her mind on revenge, nothing can stop her. For instance, she might be like Sasuke in his quest for revenge against Itachi, focused and unwavering.
Her twin sister could be really outgoing. While Hermione is often seen as a bit reserved in social situations, the sister could be the life of the party. She might be more interested in Quidditch than Hermione and be a great flyer. Also, she could be more impulsive. Hermione thinks things through carefully, but the sister could be the type to jump into action without much planning.
The plot could involve the sister seeking revenge for some harm done to their family or clan. Maybe their family was wronged by a rival village or a group within Konoha. She might use her ninja skills, which could be unique like a special jutsu passed down in the family, to take on her enemies one by one. For example, if their parents were killed by a group of rogue ninjas, she would hunt them down across the ninja world, with Naruto initially being unaware of her motives but eventually getting involved to protect her.
She could be very strong - willed, much like Naruto. Since she has grown up without her family, she has had to be tough to survive. Maybe she is also very curious about her past and her brother, which drives her to seek out the truth.
Lemon might be very kind - just like Naruto. Since she grows up with Naruto as her brother, she could have learned from his example. For example, she might be the first to offer help to a villager in need.
She could be really kind. In contrast to Draco's sometimes haughty attitude, she might be the one who is always helping out the first - years, showing them around Hogwarts and making them feel welcome.
Lee's sister might be energetic and full of life like her brother. This could contrast well with Neji's more stoic and serious nature. Her positive energy could start to break down Neji's walls. Neji, on the other hand, is highly disciplined and intelligent. He could help her focus her energy in a more strategic way in battles and in life in general.
She might develop more intuitive abilities. In some fanfictions, female characters are often depicted with stronger intuition. So, Naruto in a female body could have an enhanced sense of danger or be able to read people's emotions better. This could help her in battles and in making strategic decisions.
The sister could also bring some new conflicts. For instance, if she has a different view on how the ninja world should be run compared to Naruto. This could lead to arguments and growth for both of them. Additionally, she might have her own set of friends or allies that Naruto has to get to know and work with, which would expand the cast of characters in the fanfiction and create more complex storylines.
Her character could also be very ambitious, but in a different way than Draco. She might be more focused on academic achievements. She could be the top of her class in subjects like Potions or Transfiguration, and be constantly striving to outdo herself rather than others.
The baby sister could change Naruto in some ways. He might become more responsible and less reckless. He would have to think about her well - being all the time. For example, he might not take on as many dangerous missions so that he can be around to protect her. And as she grows up, she could also inspire Naruto to strive for a better future for the Hidden Leaf Village, not just for himself but for her as well.