Sacrifice. She may have to sacrifice her own youth, social life, and personal desires to care for her sister. For example, she might give up going to college or having a normal teenage relationship. Another theme could be growth. Through this difficult situation, both the girl and her sister will grow. The girl will learn about maturity and the sister will learn about the love and care her sister is providing despite the hardships.
One such novel could be 'My Sister's Keeper' in a way. In this story, the main character has to take on a lot of responsibility for her sister, which is somewhat similar to the concept. However, it may not be an exact match.
Another reason could be related to control. Your sister might be a bit of a control freak and sees this as a way to have power over you. She might not fully understand the implications of forcing you to live as a girl and just be focused on getting her way. However, no matter the reason, it's not right if it makes you uncomfortable.
In a boy to girl forced magic story, a common theme is moral responsibility. The boy has a moral obligation to undo the harm caused by the forced magic. Another theme is transformation. The girl might be transformed in some way by the forced magic, either physically or emotionally, and then has to go through a process of returning to normal. Additionally, the theme of justice can play a role, as the boy may have to face some form of justice for his wrong use of magic.
Well, the story could start with the sister feeling left out because her brother always gets to do 'cool' boy things. So, as a form of revenge or just for her own amusement, she forces a makeover on him. She might raid her own closet for the girliest clothes she has. She could pick out a frilly pink dress and some high - heeled shoes. For the makeup, she might go all out with bright red lipstick and lots of eye shadow. The boy would be horrified at first, but as the makeover progresses, he might start to see the humor in it. And maybe in the end, they both learn something about each other and the differences between boys and girls.
One possible consequence could be psychological confusion for the boy. He might struggle with his identity and self - image.
One possible theme could be the struggle for identity. The daughter might face challenges in defining herself given her mother's profession. Another could be social stigma, as she would likely have to deal with the judgment of others.
One theme could be identity struggle. The boy has to grapple with his own sense of self as he is forced into a role that goes against his gender. Another theme is the power of art. Despite the difficult circumstances, he might discover the beauty and power of dance.
One possible theme is love conquers all. Despite the differences in their social status, their love can overcome various obstacles. Another theme could be self - discovery. The lucky girl may discover her own strength and potential in the new environment with her CEO husband.
Another theme might be the struggle for independence. The daughter may be trying to find her own identity and break free from her mother's influence, while the mother may be having a hard time letting go. It could also be a story about family loyalty, where no matter what differences they have, they still stand by each other in difficult times.
Maybe Bella has a warped sense of what's good for her sister. She could think that the vampire fanfiction world offers a form of escapism or a different perspective on life that she thinks her sister needs. It could also be related to a relationship she has with a character in the fanfiction. If there's a vampire character she admires or is in love with, she might want her sister to be part of that world so that she can better understand Bella's feelings towards that character.