She couldn’t use the KB, but investigation showed that it was working – but with a 5-second delay before any key pressed was processed. I swapped her KB with mine and the fault stayed on her machine, and her KB worked fine on my computer.
This suggests a malfunction in the OS, but I can’t imagine what caused the problem, or how to fix it. I hope the cat accidentally reprogrammed something that led to this odd failure and can be reset without too much bother.
I REALLY hope someone can shed some light on this.