Well, for the life of me, I couldn't get it on. The chain had gotten all turned around and kinked. I'd never seen anything like it. Feeling the pressure, I undid the master link on the chain, thinking that would make it easier to get the rear wheel on. Then I'd be able to unkink the chain and rehook the master link.
Suddenly, the link slipped off the chain and down between two wooden slats on the deck where I was standing. It was 14'' below us, but it may as well have been a mile. We couldn't see the tiny link among all the debris and there was no way to get beneath the deck anyway.
My friends took off for their bike ride and Marcia offered to drive me to a bike shop to buy a new chain. When I asked the guy behind the counter for a chain, he said, "You don't need a new chain, you need a new rear derailleur!" In all my anxiety, I hadn't realized that the broken derailleur was the reason I couldn't get the wheel on. That explained the strange popping noise I'd heard when I'd put the bike in the trunk of the car!
After a few phone calls to area bike shops, I found a Campagnolo 8-speed rear derailleur - kind of a relic these days, so I'll be spending the evening installing it.
So what were the lessons learned?
1.) Be sure you're on firm ground before attempting a bike repair.
2.) No matter how much you think you know, there's a guy at a bike shop that knows more.
3.) Don't car pool to lunch - ride your bike.
My broken rear derailleur