Is she seriously considering driving that in the winter. FFS, she can’t even get into a car without hitting something.
Anyways more on topic:
Most for the ford wiring was standardized around that time frame. The power should be going to the headlight switch, from there it will go into the multi-function switch. At which point it goes to the head-lamps.
Make sure the main switch is both getting power, and distributing it to the MF-switch. In one direction it should turn the high-beams on regardless (flash to pass in some schematics), so there should be a wire that is always hot when the key is on. Which I remember correctly is one of the ones coming off the headlamp switch.
If that is hot, and you have no high-beams when you try to “flash” them then test from the MF-switch harness to the head lamps to make sure a wire didn’t get damaged/disconnected somehow.
To test the switch itself, use a multi-meter and the schematics to find out which pins should be closes when it’s in the high-beam position.