Exchange And Outlook error

One of our Employees is unable to receive email from a person from another agency. So far this person is the only one whos email is not getting through. The spam filter is passing the email through, and Exchange says the email has been delivered to the client. But the email is nmot showing up in her outbox. I can track it all the way to her computer, then BAMPH! its gone. She has no filters configured in Outlook 2000. Any ideas folks?