Some airlines have offered a "fear of flying" course, that includes a short domestic flight at "graduation".
Unfortunately, while statistics bear out that aviation is safer than car travel, the human mind sometimes has a hard time bypassing the emotional for the logical. Car wrecks which we read about / see all the time are always just a couple of people, no big deal to the emotions, but when a plane goes down it is hundreds of causalities and in the headlines for days. And for some people the emotional side of the news totally outweighs the logical side of reality.
And while drugs help calm the nerves once on the plane, you still need to convince her to get on the plane.
You can only try to appeal to her logic, through out figures such as the US airline Delta has almost 2 million flights per year, the SkyTeam alliance has some 6 million flights per year, the three major alliances (Star, SkyTeam, OneWorld) together have 17 million flights per year. All this versus a few crashes.