I'm not sure if I'm saying this seriously or not, but:

no worries! In addition to its granular permissions systems which will now let you revoke the secretary's access, Sheets also has a robust backup and restore story built-in! Just click File -> Version history and rollback the offending change. (You can do a live preview of what the effect will be, to confirm you're rolling back the right change.)

The problem Sheets has is that they built a tool that is too good :)