I've found the solution to this (like so many other questions I've had, the answer was right there in admin; I just had to find it). In case anyone else is struggling:

Admin>User Management>Access Control

There's a search module there that needs to be enabled for anonymous and authenticated users.

Really, the way Ubercart is set up, every problem I've had so far has been easy to solve, once I found the place to solve it!

Thanks for the hard work on this cart. I appreciate it!
amy