How to change a MacBook's "main" login/user?
It seems like her user needs to be enabled to unlock FileVault. See this answer on how to add users: https://apple.stackexchange.com/a/242749/45492
How to change a MacBook's "main" login/user?
It seems like her user needs to be enabled to unlock FileVault. See this answer on how to add users: https://apple.stackexchange.com/a/242749/45492