To answer the question about the KLX-250, I had a KLR-250, which was the spiritual ancestor of that KLX.
It would make a nice street bike for your wife, but it is WAY to heavy for the dirt... the weight would be way more intimidating then the power ever would be.
Power wise, it's probably a true 17 to 25 RWHP on a good day. Geared down, that's enough for the dirt until you get to long muddy second gear hillclimbs with the rear wheel packed with sticky clay. Geared up, it'll so 75 MPH on the road.
So if you want a street and gravel road type bike for her, it would be a good choice. But for riding in the dirt, I'd be thinking lighter and not street legal.