The two of you as a team... do you like bike shops or Craigslist? Thrift stores or Boutique stores?
Either head off to a bike shop together and try out some bikes and pick out one that you both like, or sit down at the computer together and start browsing websites and online ads and pick out a bike you both think will be appropriate.
If you have both a road bike and a touring bike, then get her both a road bike and a touring bike, or at least start with the road bike (or fast hybrid as mentioned).
Do you ride pavement, or gravel, or mixed?
Keep in mind, for day trips, you can carry all the lunches, gear, spares, etc, so she could be on a pure road bike.
One thing to keep in mind is that different people have different feelings about riding in traffic. Traffic can be very uncomfortable for certain older newbies. Figure out what you need to do to make it comfortable. Good roads? Designated bike routes. Park & Ride? Mirrors? Keep her right, and you can pull to the left for side-by-side, etc.