You need to drain the tank (at least most of the diesel fuel), fill the tank with gas, (don't let your wife do this part), then remove a fuel line from the injectors and crank the car to pump out the pure diesel in the lines. Reconnect the fuel line and the car should be fine.

A bit of diesel in a gas engine will not cause a problem, I ahve found that a litre in a ful tank seems to help keep injestors cleaned out.