If fem Sasuke became Naruto's servant in a fanfiction, it would be a huge shift in their relationship. Naruto would likely be protective of her, not really seeing her as a typical servant. Fem Sasuke might use this situation to her advantage in some ways, like getting closer to Naruto to learn more about him or his plans. There could also be a great deal of character development for both of them. Naruto might become more confident in his leadership role, while Sasuke could become more empathetic through serving Naruto. And of course, there would be many fans who would be excited to see how their relationship progresses in this new and unique setup.
Well, it could lead to a whole new dynamic. Fem Sasuke might initially resist the servant role with all her might. But as time goes on, she could start to understand Naruto better and develop a different kind of relationship. Naruto would have to deal with the fact that his old rival is now in a subservient position, which might make him uncomfortable. There could also be a lot of comical moments, like when Sasuke tries to do normal servant tasks but does them in her own unique, Sasuke - ish way.