Final answer:
Sophie creatively transformed the big red F on her black robes, likely turning it into something positive or artistically expressive.
Step-by-step explanation:
Sophie appears to be a creative and resourceful character, making the best of her situation by repurposing the big red F on her robes. While it's not explicitly stated what she does with the red F, we can infer from the context provided that she may have transformed it into something positive or artistically expressive. Given that the provided texts describe characters engaging in creative acts, such as draping fabrics around themselves and converting failings into success, Sophie might have engaged in a similar action of transformation or artistic endeavor.