How nice to have you back on the message board. We've missed you.
As to your questions, you might start by contacting the Navy Memorial in Washington, DC http://www.navymemorial.org/. (As you may know, the Memorial includes a commemorative plaque jointly honoring the Armed Guard and the Merchant Marine.) In particular see the "Contact Us" link at the bottom of the home page; a retired Navy vice admiral, John Totushek, is the president and CEO of the Memorial. Maybe he would have some ideas or even some contacts. Just by the way, I see that your father's name is included in both the "Navy Log" at the Memorial's website, and at the website of the National World War II Memorial. Good for you.
Or maybe the U.S. Navy History and Heritage Command (http://www.history.navy.mil/) could offer advice. A Captain Henry J. Hendrix II is the current Director of Naval History.
You are probably correct that the final say is up to France. So you might try contacting either the Embassy of France (http://ambafrance-us.org/) or any of the ten French consulates around the country (in Boston, New York, Atlanta, Miami, New Orleans, Houston, Chicago, Los Angeles, San Francisco and, again, Washington, DC) in case your sister is contemplating an in-person visit to present her idea. Perhaps one could start with the cultural attaché and/or the defense attaché at the Embassy.
Good luck and best wishes.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website