have you been using baking soda to either clean this tub or has your wife been taking baking soda soaks?
You still MUST have an electrician look at it, no doubt about that, but, while you're waiting for him to show up, if you have been using baking soda, stop it. I have absolutely no idea why, and I'm not sure if we have a resident chemist here who could explain, but my kitchen faucet (on a porcelain-over-cast-iron sink) used to give me a slight tingle-type shock (sort of like what a 9-volt battery will do to your tongue if you're silly enough to test it that way). The sink is nowhere near an electrical outlet, and no wiring is in that wall. As soon as I stopped using baking soda as a scouring powder (the plumber gave me that advice) and got all residue completely off, it stopped. Coincidence? Maybe, I have no idea. I just know I no longer dread touching the faucet.