Hi, I'm Robert and I'll be helping you with your computer question.
check in the deleted folder
and also check the filters. if it is set to show only important emails or only unread emails they could look like they are gone
or if she filed them into different folders that would do it as well.
If it was a time gap the most likely reason is they were downloaded to another device. Either by pop that stripped them. Though gmail default is not to. Or imap and deleted on the device which deleted them in gmail
You can ask google to recover them for you
But they will only do it if you say that you lost them because ypu were hacked
Use this form