The solution was easy, one of those that comes to mind just before sleep. I located the fax .plist, removed it, restarted, and voila! Faxing tab is now accessible.
...but it is still blocked. Here is the re-submission of my question. Maybe this explains it better:
10.4.X (Tiger)
PLATFORM Apple Macintosh (PowerPC G4)
MODEL Mac Mini G4/Power Mac 10.1
PROC 1.41 GHz
RAM 1 GB
DRIVE 512
I have the exact same computer, unplugged my mom's, plugged in...
I was just setting up my mom's fax preferences. Clicked the option to show fax status in finder bar, then clicked "sharing" tag. The "fax" tag went gray, and now I cannot access it.
How do I get it unstuck?