The crux of "In the Waiting Room" is really the National Geographic magazine itself. Elizabeth seems quite proud of the fact that she can read this magazine for grown-ups at such a young age. It's her reading experience that opens her up to this whole new world of volcanoes, explorers, African people, etc. Let's just say that it's a good thing that the dentist's office had such interesting material. If Elizabeth were stuck reading Highlights or Soap Opera Digest, she probably wouldn't have had such an intense experience.
Photographs are more powerful than words. Elizabeth reacts to the photos she sees, not to the articles.
Words are more powerful than photographs. Bishop wrote a poem about this experience – she didn't take a photo or make a painting of it.