I'm a roadie, but I did buy a mountain bike from W - M for $97 with 21 speed indexed shifting. I bought it simply because we do camping and the kids have bikes and decided I should join in with them. The bike is somewhat heavy but rides and shifts really well. No problems at all from day one. I actually enjoy riding this bike - jumping over stumps, curbs and doing stupid stunts I would not dream of doing with my Bianchi Giro roadie.
I think you or your wife should have tested the bike out first before riding it. When I bought my W -M bike I tested the thing out first in the driveway. Mind you I know what to look for for problems.
Moral of the story is make sure everything is working before doing a ride. Actually, I do that everytime I go for a ride. Check the brakes, tire pressure, whell alignment and etc.