Spring for a really good steak from a reputable butcher shop. Talk to the person behind the counter. They can also give you some pointers.
I agree with the KISS idea: Keep It Simple Sweetheart! Sprinkle a few grains of kosher salt (or if you're really feeling like splurging, fleur du sel) on top of the perfectly cooked (and rested) steak.
If she'll eat potatoes, try taking a nice baking potato and slicing it across the length into thin slices ALMOST through to the bottom. Gently and carefully fan it out a bit to slightly separate the slices of potato, then sprinkle in just salt and pepper or some herbs or, if you know she'll eat it, parmesan cheese. Drizzle with melted butter, wrap loosely in foil, and bake about an hour at 350 degrees for 45 minutes or so. Unwrap and let it brown a bit for about 10 minutes. Looks really classy, but it's just a dressed-up baked spud.
If she won't eat veggies, will she eat a salad? If not, don't push it.
The best thing you can serve her for dessert is a heaping dish of respect!

Good luck with your menu and your evening! Let us know how she likes your meal.