Death and a child

May 2021
I'm a writer and need some advice. My main character (Mel) is a child and she has a twin sister. One day that twin sister dies but no one tell Mel. Mel sees her twin sister, imagine her, as if she truly was here, but only her see her. Her 'twin sister' says that it's because they are playing a game of hide and seek and that she only allows Mel to know where she is but that she isn't allowed to talk about her hiding place to anyone. Her family knows about it but does nothing because they think it's better that way. Mel grows up from a child to an adult, still believing that her twin sister is alive and playing a game.
Is that situation plausible? To think for years that someone is still alive.
Thank you!