Greetings.

For no apparent reason, my wife's laptop restored all software to original factory settings. Microsoft Office is no longer installed, Explorer points to original welcome screen, etc. Desktop has reverted to original Dell logo.

The good news is that all her files are still there, including .pst for Outlook - even though Outlook no longer exists. And happily system restore does recognize numerous previous restore points, the most recent being 3 days ago.

The only thing we can think of is she made a rare visit to a non-secure hotspot about 10 days ago. Virus?

WOW! never heard of this....it she absolutely certain she didn't hit some key or key combination which restored the computer to it's original settings? I have never heard of a virus or trojan that would do this.
Give us full info on the computer...OS, anti-virus program, internet connection...everything you think we would need...maybe even what you don't think we would need.
Is she absolutely certain she didn't do a Repair of the os?