Lucky you didn't post this on fbook that your wife's high-beams need attention. We are much more mature here....snigger
Check the basics every time. There's grounding for the headlight harness on each end of the radiator support, also a ground cable off battery or similar to support. The dimmer switches are cheap and fairly universal, good to have a spare or two just to swap over and test. Also, check the actual lights, are they original style sealed beams or swapped to halogens etc? That would also usually require a rearrangement in the wiring at the plug and many don't do it, leading to problems later. Likewise, slow overheating of the headlight switch at the plug can result until it parts ways after incorrect lighting used and excessive current draw. This can be overly powerful high beams or regular lighting used more often. Rewiring to use relays prevents these issues but helps to know what's going on first and why.
My own car came swapped with halogens, had a set of conversion harness plugs in the spares box which confused me for some time as to their use, and later found the headlight plug terminals all melted, but taped to hold in place. Nice repair. And then it starts to become clear why.
