Ensure deleting a section is recoverable
My niece has just lost a whole semester of study notes when she inadvertently clicked Delete Section instead of Delete Page. Undo did not work, and the pages were not in the trash either on her Mac or on OneDrive. This is an appalling hole in the OneNote product!!! You must update OneNote so that it is possible to recover a deleted section, at least for a few days. She tried immediately to get the section back, but it could not be recovered.
Did she check the auto-backups? May be too late now, but one note makes backups automatically. Find the link to the folder by going to the File Menu then options then save and backup. The backups are over written with time. Check sooner rather than later!