in the story it is mentioned that she has almost completely forgotten what happened in her previous life and remembers the story as a story and that she only has the memories of these six years so she is basically a child so it is not strange that she behaves like one
It's only a theory of mine. But I think she thi KS of her past life as a book(it was mentioned in one chapter that she does not know why she read a book like that) so she basically is a child that's smart and has never got to act like a real child , so now that she has love and protection she acts childish.
PLEASE TELL ME IF SHE'S STILL ACTING IMMATURE AND ACT LIKE CHILD. BECAUSE IN THE FIRST FEW CHAPTER, IT'S BOTHERING ME