It was school assigned, she said all of this before, she said her parents didn't want her to have one,

This means the iPad was given back to the school at the end of the year or whenever she left, and wiped. This means unless the next student the iPad was given to plays graal era on it, the account would never have been played on again., meaning most likely it's someone hacking the account and pretending to be Mayu, and getting away with stealing her account.