Answer:
Even though Reb Moshe Feinstein zatzal wrote that one may kasher and use a stainless dishwasher if you replace the racks, for practical reasons it should not be done. First of all, the tracks for the racks usually have plastic parts that cannot be kashered. Secondly, particles of food can easily become trapped between the runners and the walls of the dishwasher, and hagala does not help unless all the mamshus is completely removed. Finally, the drain filter and pipes where the dirty water exits the dishwasher are full of residue, and on most models cannot be thoroughly cleaned. When running the unit, it is very likely that hot water could back up from the drain into the chamber and render all the dishes and silverware treif.
I would suggest you tell your wife that you asked a Rav who said that Halacha does not permit using the dishwasher, and it is not just a chumra.
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