I had the same thing happen to me once this summer with my 95 E320, pulling into a parking spot. It flustered me a bit until I realized, while braking my foot was also pressing the gas pedal.

Historically - and this is speaking from what I know about the Audi problem in the 80s, after the problem finished splashing on the headlines - the problem is psychological. It is incredibly difficult for the driver to believe he is making an error with the pedals when his brain is telling him that his foot is standing on the brake pedal. That's why there were so many people who steadfastly insisted there was something wrong with the car. This problem extends to other models and incidents as well.

I offer that your wife may not realize she is touching the gas pedal while braking, especially if her foot is on an angle, as mine is while driving. Stories by 'witnesses' can be notoriously unreliable. Can you replicate the problem?

I understand today's vehicles are designed so there is about a two inch separation between the brake and gas pedals, and the brake pedal is two inches higher than the gas pedal. Perhaps the brake pedal has too much travel from air in the lines.