Wife and I are just getting into MB... I used to ride all the time as a kid, but it was all in town, no offroad stuff, so it's all new to me too. The wife, try as she might, has never been a well coordinated athlete.
That said, we got a pair of entry level FS bikes from Diamondback. We don't ride anything too hard core, and I doubt the wife ever will - and who am I kidding, at 40 I won't either. Moderate/Intermediate will likely be my peak.
Anyway, we took them out last weekend to
Hill Country State Natural Park near Bandera, TX. Rode easy trail 1 from the "bottle opener" Parking lot (which was mostly twin track, varied between grass/dirt/rock) almost up to the Wilderness Camp area, the went back the same way to trail 5A. We took 5A (a more difficult single track trail) up to the scenic overlook. I could have rode it, but the wife couldn't. She was pooped, and after a break to eat a Cliff bar walked her bike up to the overlook (I walked mine with her). But I was pretty proud of her for riding the whole trail back down.
I've read this park is not too challenging for seasoned riders, but for beginner up to intermediate riders seems to be a good choice. It is shared trails between Hikers/Bikers/Horse riders. If you go and need a place to stay, I highly recommend the West 1077 Guest Ranch, which backs up to the park. Their breakfast and lunch are very good (they don't serve an evening meal), facilities are clean and well kept, and the owners are good people.
Edited: Removed bike pics because they were HUGE. You can look up Diamondback Recoil 29 in google images if you want to see what we ride. Mine is gray, hers is white.