Go rent a Harley, Gold Wing or similar (or not
) and take a nice ride with her where she can get comfortable with the physical as well as the psychological aspects of riding. If she is wanting to continue, go shopping and test ride together
if you intend this to really be a 2up long distance pick. There are a ton of great buys out there, but it will be wasted $ and more importantly a lost opportunity to get her hooked into the enjoyment of riding if you choose based on anyone's arse being happy other than her's
My SWMBO used to ride with me all the time and if she still would, it would absolutely dictate what my next bike would be as it was a whole different and positive aspect to my motorcycle travels that I am glad we shared.
Best of luck!