Update... My neighbor came and got her machine tonight. I didn't feel like I knew enough to take that knob apart. Looked like I'd have to remove the shaft from the back. She's going to visit her daughter, where there's a Viking dealer, and will see if they can help her.
Sometimes sewing machine maintenance can have some down right funny stuff. Another one of my favorites is the "felt blanket" under the feed dogs. You know... when she says, "my fabric won't feed through."