I was just reading an old issue of MBA (Mountain Bike Action) the other night on the throne that discussed this very topic. I don't remember the month of the issue, but it's the one with the Storck Carbon Fiber Full Suspension on the cover!
Regardless, the article gave tips on taking your girlfriend/wife/sig.oth riding for the first time.
Many made a lot of sense, and the following are some that I remeber (forgive me if not completely accurate)
1. Don't inundate her with tips and suggestions. Let her experience the joy of learning and finding things out on her own. Give tips, but don't rattle them off one after another!
2. Plan the ride to end up at a picnic (as mentioned above) or make the ride an especially scenic one.
3. Ride at HER pace, and if she has to get off and walk a climb or a section, YOU do the same. IOW, don't go bombing down that technical descent thinking you'll impress her while she walks down. You'll just frustrate her!
4. I can't rember anymore, sorry!
L8R
__________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger