What to do depends on how mobile your DW is. If she has trouble hiking, you can drive and see a lot of the park, but it requires hiking to see the majority of the park. My ex couldn't hike, so we drove every road we could, needed 4 x 4 high clearance vehicle for some of the roads and saw a lot of the park.
Do you need fhu or can you dry camp, when are you going? There is only 1 fhu cg in the park, the Rio Grande Village. The other Rio Grande Village cg is run by the NP and is partly no generators and partly generators allowed. Chisos Basin is length restricted to about 25 ft., the road up has a couple very tight switchback. Cottonwood cg is no generators.
There are several cg's outside of the park, that are fhu, but add considerable travel time.
more information from you will get you more answers, also if you do a search on here for Big Bend NP, you will get tons of info.