What was it about the road bike you didn't like? When you mean standard derailleur, do you mean the old-style friction shifters? (meaning you had to finesse the lever to get in the right gear) was it the balkiness of the shifting that interest you in the NuVinci? There are fine indexed derailleur systems that don't feel as balky as the friction shifters if that's what you're aiming for.

Truth be told if she's an avid cyclist and on a lightweight racing frame, you'll have a tough time keeping up on just about any upright bike. That's not meant to discourage you, just that with any bike you pick, it's mainly going to be on her to ride a more relaxed pace when she's hanging out with you - so I wouldn't sacrifice to find the lightest fastest frame you can. You can keep up a brisk pace on a suitable hybrid bike. It will be heavier and a little slower with wider tires tho'. But you get a more upright position and the bike will feel more "substantial" if that's what you're looking for.

You should definitely try a recumbent if you can get the chance. By the sound of it you're mostly riding on quiet rural roads, so it might be just the ticket.

Good luck, and welcome to BikeForums!