When arriving in Geneva on an international flight, you are not able to exit directly to France, but will have to go through Switzerland. Exiting directly to France without going through Switzerland is only possible if you arrive on a flight from a French airport.
From the airport's web page:
Is it possible to exit directly from the French side when arriving on
an international flight without passing through Swiss territory?
No, you must pass through Swiss territory from an international
So if it is right that your wife needs a visa to enter Switzerland, she will not even be allowed to board the plane to Geneva without having one. Depending on what is less inconvenient, you will either have to get her a Swiss visa or fly to a different airport in France.