Not sure on that era CC, and as you know, the Concept's are a bit unique! But many of the valves used in the showers have extra valves to keep from scalding. You might take of the trim around the valve, see if this valve has the mixing screws. If so, turn of the water pressure (ask me how I know that) - and open the screws to see if you have build up clogging form that area.
If not, then it's poking around in the belly to see if you can trace water pipes back and make sure no problems in the piping feed... As I'm sure you knew
A good story to look back on and laugh in the future!! Next time, hand her out the soap and shampoo and let the rain take care of the 'stuff' from the pigs!!!
Best of luck and please let us know what you find out,