I suspect the math is a whole lot more than that. An actuarial would be required, and they would have all kinds of data points to collect and access.Your wife may be an expert psycotherapist, but a mathmetician she is not.
The average lifespan for women is higher than for men. Ergo, for men that outlive their wives, they will outlive them, on average, by less than women that outlive their husbands.
She's drawing a false conclusion from the overlap of two bell curves.
One example is even the average life expectancy of Americans is reported to vary be region. If accurate, is it the climate, available healthcare, water supply, dietary trends of the region?