First, thanks for the great advice so far. I'm excited to be a part of this community!
Stick around. You'll find that we each have personalities: some that you will like, or will drive you nutz
I'm starting to understand some of my mistakes.
Some of us are always trying to understand our mistakes... that's part of the fun of sailing.
Post here often, and people will point out mistakes that you didn't even know that you made.
...The result is the boom and the sail were basically sitting on our lap and we had to maneuver under and around it the whole time. Not being comfortable in the boat eroded our confidence in what we were doing.
That does not sound like fun to me... It would be a pity if you or she gave up after one bad outing. Think of sailing like snow or water skiing. The first time is not very fun, and you fall more than you ski. However, after a while it becomes second nature. With some of us, it becomes an obsession
The CE, or center of effort makes perfect sense. I suspected that that was the problem when I was on the water, but did not know how to put it into words. So how do I find a good CE with only the mainsail up?
You can not! If the boat was designed to have two sails, then it will only be balanced with two sails. With the jib alone, the CE will be too far forward, and the bow will get pushed leeward. With the main alone, the CE will be too far aft, and the stern will get pushed leeward (called "rounding up"). If you round up a lot, again the wind will push you leeward. Neither of these are fun, or effective at getting you where you want, or need, to go.
I will suggest that you and she take a lesson in sailing on a larger boat. You'll get more out of a 1 day lesson than you think. Also, it should not be too expensive (it will certainly be cheaper than a motor), and you will learn the basics. You could also find someone to take you or her out in your boat (it looks a little too cozy for three), and learn the basics of your particular vessel.
...We did have fun before we realized we could not get upwind. It was very exhilarating!
The fun only increases as you feel more comfortable with the boat!