Short of a formal program, my 100% serious suggestion is to point your friend at the "Ask a Delta Pilot" thread in this forum that W0X0F_2p2, a Delta pilot, very generously maintains in his spare time as an unofficial resource.
On one hand, W0X0F has been kind enough to answer basically every question you could imagine about how aviation works - weather, avionics, safety, air traffic, and the business side of flying have all been covered at some point. By the time your friend finishes that material, he or she will have a much better understanding of how flight works from a mechanical perspective, and demystifying that is the first piece of the puzzle.
More importantly, though, they'll have a much better appreciation for who's behind the controls of the aircraft. I think, at least for myself, my biggest concern is instinctively whether I should trust the folks in charge of the plane... let's face it, the safest strategy when driving on the road is to assume all the other drivers around you are idiots, and that is proven to be the case in unfortunately far too many situations - so it's natural to be concerned about the same thing when flying.
In aviation, it's completely different, though - pilots flying commercially for a major airline like Delta have years of practical experience and undergo frequent requalification training. Perhaps even more reassuringly, they come to the airline with extensive experience as hotshot military pilots of high performance aircraft as well. These guys and gals really are the most qualified out there for the job, the best of the best in their field.
Putting a face on that generic pilot persona, it's impossible to come away from reading W0X0F's well thought out, articulate posts without forming an impression of him as competent, thorough and trustworthy - exactly the qualities that reassure me as a frequent passenger.
Your friend may even want to consider registering an account and posting a question of their own - that thread is a golden opportunity to clear the air of any lingering concerns or reservations they may still have about air travel, too.