It is 90% psychological, but that does not make it any less real. Have your bride eat a good stomach filling meal of liquid absorbing food before a flight. Avoid liquids, especially coffee. Liquids slopping around in a stomach, combined with a little bit of fear, is guaranteed to start filling burp bags.
Then there are people who flat out do not like to fly, nothing you can do will change that. You might want to consider that your new toy is your new toy, not hers.
If you bought your airplane as a means of travel for both of you, you might have just thrown your money away.
I also think that you think your wife does not trust in your aviating abilities, so you might be trying to prove your abilities to her. You are finding it upsetting that she does not want to give you the chance. You are probably also upset that she is not worshiping the ground you walk on, in all things that you decide to do, you're forgetting that she is an individual person, not part of you.
Not all pilots get to have spouses that love to fly, and it frustrates many of them. The ones it does not frustrate, continue flying, and having fun on their own, the rest eventually give it up.
-John