Outlook deleting emails every weekend

I have a user that her emails are getting deleted automatically somehow every weekend, sometime Saturday night, as she says that they were there Saturday evening, but on Sunday, they are gone, it's happened for 2 weekends now.  I've looked at the rules, and I didn't see a rule that would delete any emails automatically.  Where do I even begin to look at to fix this issue?  How do I know if it's Outlook or exchange doing this?  No other user has reported this yet.  She is running Outlook 2007 and I'm using Exchange 2007 with SP2.