Diesel in Gasoline Tank - Long-Term Damage?

My GF’s Corolla, which is 7 years old but has low mileage (49K), reportedly needs a new catalytic converter. Before she bought it (used), the previous owner, a family member, accidentally put some diesel fuel in the tank. A thorough cleanout was done by Toyota at the time, but they advised the family there could be unknown long-term effects.

I’m guessing the diesel event probably hastened the demise of the converter, but I’m still wondering if this isn’t a premature failure. What else could contribute to early failure?

Need more information. When the diesel was in the fuel tank, did the car continue to run or did it stall out.

Get a second opinion on the catalytic converter. It shouldn’t be bad at this mileage.

Not enough miles on the car, so I think that too much low speed driving could have contributed to the failure. No need to take this answer too seriously. Guesswork is iffy. Some of those things just go for no reason.