There's only a few things I can think of, but part of me feels like this might be a trap... ah, who cares, I'll give it a go!
- Madelyn's love of writing mimics Ella, aside from Madelyn being a professional writer
- Zorro#34 pointed out that Madelyn and Lily's eyes are present in the loading screen that just so happens to contain the three main LIs (this might be a red herring)
- The end sequence with Madelyn feels a bit too on the nose with her stating she "would never dare to even try taking someone's place", only for Gregory to immediately encourage her to do just that by "being herself" (i.e. be like Ella)
As for Madelyn's intentions being nefarious, I'm not sure she has any ulterior motive with the MC considering she didn't really know about his existence (and by contrast neither
did Charlotte until she researched his company). In some ways she resembles a young Ella who was rather isolated and forgotten, and as
Gregory states "even as some things are lost to us, others are found". It feels quite symbolic (almost literally) that Madelyn is the MC's missing piece, and vice versa.