I spotted that too. But I think it’s not so much an imaginary friend as it is a Lottie in her head. My theory is that she’s an obsessed fan who’s developed a parasocial thing and walks around talking to her “best friend.” She’s probably here to solve the same mystery so that the real Lottie will know who she is and instantly think she’s great.

The question is what flipped her obsession from love to hate. Lottie and Claire beating her to the solution? Lottie being rude to her in some fashion? We’ll find out.