Hi,

She doesn't look at her mails through say, an Unread search folder does she? Can she see "read" emails? I assume so, but its good to check.

Is her Auto Archive the culprit? To check click the Folder tab, then choose AutoArchive Settings, and look at the settings. You'll have to do this on each computer that she uses.

If that's not it, then maybe running the Inbox Repair Tool (scanpst.exe) on her pst or ost file might fix any errors that might be there.

If that fails, create a new Outlook profile for her. Wait two weeks. See if the oldest emails are disappearing. If so, it's something at the server level.