The solution to that one is easy. Let the person go through the WTMD, and when (if) they alarm, give them the SSSS treatment, and send the heels through the x-ray after they alarm on wanding. The pax will then learn that her shoes (or, in the case of men, many dress shoes with metal in the soles) will alarm, and won't make that argument again.

Making everyone take his or her shoes off for no reason other than the knee-jerk, horse-has-already-left-the-barn reason than "someone tried to blow up a plane with a shoe bomb!" kabuki security should not be seen as solving the "problem" of idiotic pax.

(Not to mention that it's quite possible the amount of metal does not set off WTMDs at many airports but might at others--so the pax might not even have been clueless, or as you put it, "retarded." I know my typical business-casual shoes have enough metal that pre-8/10 would trigger the WTMD at about 40% of airports I traveled through, so I usually removed them, but there were plenty of airports at which I also knew I could keep them on with no fear of setting off the WTMD).