I wonder, since the mysterious person is obviously Elsa somehow, why didn't she go back in time further and prevent the stabbing incident at the beach? Is it because it ultimately wasn't that harmful, and that she'll only step in if it is?
I'm re-reading it, and I now remember that she appeared in her dreams. I really wonder why did she went in the past to remind Yvonne. There's something to do with the Dark Magic and Villainess System (Original Yvonne). There's a possibility of Yvonne's death that made Elsa went back the past which is now