My sincerest thanks to your husband for serving our country and to you for your sacrifice while he does so.
Unless the engine is having severe problems, like burning oil by the barrel, there’s nothing that would make it go bad immediately like this. The only real thing that kills cat converters and oxygen sensors quickly is if the surfaces get coated. It’s the surface contact with the exhaust stream by which they do their jobs.
It is possible the incorrect oxygen sensors were used. Your husband’s friend would not be the first to make this mistake. Perhaps a shop with a scope can look at the traces.
Guys, any other thoughts? I could use some help here. We’re helping a military family. She deserves our best…not just my rambling thoughts.