Omg just a random theory but... What if the Eclette is actually her younger sister's reincarnation?
My gut tells me the sister (the author) is probably dead (because MC/Shaylia talks about how this must be a second life her sister gave to her, which would be a weird thought to have if the sister is alive; you usually only attribute supernatural things to dead people with the consideration that they are watching over you in heaven; there was also that panel with her phone in the Prologue that talked about her sister's medical fees), and it seems like this story is going down to route where MC takes care of the princess like a little child (maternal, or perhaps sisterly instinct?). It would be really lovely if there's a twist where the sisters actually unwittingly reunited in their new lives.