message body suddenly not visible in Outlook Express emails

I'm writing on behalf of my sister-in-law, who owns a Dell (probably Dimension) running Windows XP and Microsoft Outlook Express.  She has owned the computer about a year and wasn't having any email trouble.  But just in the last day or so, she has been unable to view the message body of any of her emails.  She can still receive emails and she can still send them.  Her Outlook Express display shows the current open mailbox's contents (Inbox or Sent Mail or whatever, doesn't matter).  She also has a preview pane, but when she clicks on any email (even ones she received and read long ago), the preview pane displays nothing.  If you put the cursor over the preview pane, it shows an hour-glass, as if it's off doing something.  The hour-glass does not display over any other window and other applications are not impaired, and the performance meter does not indicate high CPU usage.

If you double-click on an email message to open its body in a new window, the window opens, but the message body does not display.  Again, the hour-glass is visible if you put your cursor over the message body window.

Here's the more-weird thing: If you reply to sender (and her preferences are set to automatically include the message body in the reply), the compose reply window will pop up, and in that window you'll see the header of the included email message, but again, the message body will be missing.  Only this time there's no hour-glass; it's as if Outlook Express is completely satisfied that the inclusion is complete.

She can, however, still read her mail, though through a pretty torturous process.  She can click on the message properties (under File) and click on "message source", and the message will indeed display, including the message body text.  I have no idea what you'd see with an attachment in that view, egads.

Her ISP is comcast.net, but I don't really think this is a Comcast problem.  Her account at their server site looks totally normal and nothing appears wrong, like I said, with sending and receiving.  I was able to email myself from her computer and get the email just fine.

The only other clues I can list are (a) she did try deleting her cookies lately, and perhaps in that process she might have inadvertently deleted something important, though I'm pretty sure she did that several days ago.  (b) she has a four-year-old who might have typed god-knows-what into the computer.  He is madly attracted to the mouse and has in the past dragged innocent folders to mysterious new homes.  Though again, I have no indication that he spent any quality time with the computer in the last couple days.

Does anyone have any clue what's up??  I am worried it might be more than just a technical malfunction because of the weird behavior regarding reply inclusions.  But she has both up-to-date virus scan software (pretty sure it's Norton) and has downloaded all the recommended Microsoft security patches.

Help??  Thanks!

Jenn