It could be that the kidnapper believes the horror stories might have some hidden meaning or code. They might be looking for something specific within the stories, like a location or a name. For example, if the girl has some secret knowledge, the kidnapper thinks the horror stories could be a way for her to unconsciously reveal it.
One possible reason could be that the kidnapper is a sadistic person who gets some sort of twisted pleasure from hearing horror stories. Maybe it's part of their sick game or way to terrify the girl further.
One possible reason could be revenge. Maybe the girl felt wronged by the boy or his family in some way and decided to kidnap him as payback.
One possible reason could be for ransom. Some kidnappers target girls from wealthy families, thinking they can get a large sum of money in exchange for the girl's safe return. For example, if a girl's parents are business tycoons, the kidnapper might believe they would pay millions to get their daughter back.
One reason could be revenge. Someone might want to take revenge on the boy or his family by changing his gender. Another reason could be a crazy experiment. Some mad scientist - like character in a story might think it's an interesting experiment to see how a boy would adapt to being a girl.
One possible reason could be for attention. Maybe she felt ignored in her daily life and thought that such a dramatic story would make people focus on her.
Love or obsession could be a motive. Just like in some stories where a girl is so in love with a boy that she kidnaps him thinking it's a way to keep him close.
One reason could be for self - expression. Makeup allows her to physically transform herself, and horror stories are a way to express her creativity in storytelling. She might be attracted to the dark and mysterious aspects of horror, and makeup helps her bring those elements to life.
One reason could be for religious purposes. In some religions, shaving the head is a sign of purity or a part of a religious ceremony.
Lack of resources. For instance, in a theater production, if there are not enough female actors, a male actor may be forced to play a girl's role.
It could be a part of a creative writing exercise. If she is into writing, she might be exploring different and edgy themes for her stories. For example, in some advanced creative writing courses, students are encouraged to step out of their comfort zones and write about unusual or controversial topics to develop their storytelling skills.
One reason could be the vivid imagination. When reading horror stories, our minds create terrifying images easily. Another is the fear of the unknown. Horror stories often involve mysterious and unpredictable elements. Also, some people are more sensitive to the negative emotions and atmosphere in horror stories.