I think ..it's ok to wrote story like this..
maybe she thought this ending will be strong enough to make others says : WOW
IT'S SCARY BUT i wrote story like this when i was 6 maybe
i killed the boy ( Ahmad) in the end xD AFTER i tortured him with such drama
don't worry, your sweet little sister exploring the world of deaths and the unknown one with a pictures in her mind
what did she told you about the idea of her story ?
i hope happy ,white and shiny life for your sister
don't forget to improve her talent

thank you spring lover .. be safe