Password expiring message just before Welcome screen

I helped my sister upgraded over her Dell OEM Windows ME to retail Windows XP Pro SP1 a few months back (she didn't want a clean install), and now there is this message saying the password will expire in 7 days and ask whether she wants to update it.  If she clicks NO, Windows continues with the Welcome screen and normal operation.

This computer is a stand alone computer and not on a network (although the NIC is connected to an ADSL modem).  My sister is the sole Windows login user (apart from the hidden Administrator account), and she doesn't require a password to login.

I suspect this may have something to do with her previous Windows ME network setup - her accountant did all the work.  If she doesn't change the password within this week, this "password" will expire and I'm afraid she would be locked out.

How do I remove this password?  She doesn't want to be asked every so often to change a non-existent password.

Thanks so much!