It may be that this woman knows something we do not know. We think we can not wash the car with water pressure inside because upholstery would ruin. But we do not know, because we have not tried to never do.
We also think in electronics. The stereo is not waterproof. But neither know, nor because we tried. I mean many things we think may be erroneous, and in fact are not.
One thing is certain. The car will be very clean. And if the car is her husband, this will kill her when he steps into the car.