Or you could just say "Honey - You're going to have a fantastic time!" because you know you will be riding on fat powder skis provided by Steamboat Powdercats and they will take care of all necessary powder technique instruction.
I don't know which models of Armada's SPC has and I haven't seen intermediates ski powder on the newer fully rockered skis, but I have seen a bunch solid wedge christy wives outski their powder experienced parallel turning husbands because of the super fat skis we were on. The ladies just skied like they were on a perfectly groomed slope and had a blast. The guys tried to bounce and all they did was get their skis stuck in the snow and lose their balance. With fat powder skis you trade some of that skiing "in" the snow feeling for "ease" of adapting. Rocker technology enables parallel skidding in powder so those ought to be even easier. I can't imagine that the "beginner" cat is going to be too tough for this strategy to work.
Have you tried asking the "cat people" for their recommendation? Or just looking through their website? Their site does a good job of covering it all.
But if you insist...
Powder skiing is all about making adjustments. You can try practicing skiing more two footed with your skis closer together making turns more down the hill than across the hill. You can even try practicing making turns in "slow motion" and controlling speed through turn shape. But as Kevin has noted, the biggest change is from the neck up. You can't practice managing your internal speed limit for the extra friction that skiing in the snow provides and you can't practice managing your vertical position within the snowpack. You can practice tree skiing, but you really won't need to. A beginner cat tour will either not do trees at all or you'll find trees that you could practically straight line through. The solution to the mental problem is low stress mileage. There's a reason these guys offer a money back guarantee of success. If you already know how to ski at the intermediate level, it's pretty easy to just show up and have fun.
One thing you should prep your wife for is the safety protocols. Group dynamics is a major contributing factor to back country accidents, but it's probably the least emphasized point in the safety briefings. Make sure your wife knows that if she hears the little safety bird chirping on her shoulder that she SHOULD speak up, but that she should not be making snarky comments about luke warm hot chocolate. When you buddy ski, take turns leading and let her know it's ok if she peeks back to check on you now and again. Avy beacon training can be scary for a couple of reasons (e.g. is it really that dangerous? there is no way I'm going to be any good at this), but driving to the airport is more dangerous than professionally guided back country skiing when you trust your guides and follow their directions (no stats - I just made this up to make you feel more comfortable :). The more your group pays attention to your guides, the more "leash" the guides will give you on your runs. Don't let the words "hurry up and wait" bother you.
Don't worry. The snow around Steamboat is about as idiot proof as it gets.