it seems the Rich girl who pushed off the girl from the cliff has literally declared that Banri is dead by some means. (Banri is the name of the girl that fell off the cliff)
Her father is a politician so she may have made some funeral arrangements in advance and told her parents she died etc,
in the last scene she is burning her documents and possibility her birth certificates or something which if lost might declare her as being an alien (unknown individual) in the country and thus by extension being even declared dead.
however Banri is alive is already seen with Momo in school and shows her a creepy envelope she received from the rich girl while still in hospital.
as it turns out, its a check for funeral arrangement funds and the reason it looks creepy is obvious its meant for a dead person.