Why did I have the same thoughts when I was reading like if you look at the writing style of going back to the past multiple times the implication that the original fl transmigrated/went back as well it wouldn't be out of character for the story to take such a change 2) her loss of memory is very suspicious and I think that the languages would explain if her lineage is of both royalty and the goddess chosen person 3) her looks she is the only one in the story so far that looks similar to the ml so I think that wouldn't be so far of but thats just a theory a manhwa theory ⁄(⁄ ⁄·⁄ω⁄·⁄ ⁄)⁄
I think selene is their child in future..maybe she's a time traveller,she wants to help both the ML and FL to avoid the bad future that they will encounter,but she lost her memory while time travelling...it's just my thinking...