Wow, either she slipped into an alternate reality and crossed over or she too was hallucinating (which I doubt). However, I see 2 reasons for it;
-either it was tied to the old woman, as it only happened to her OR when she was with Amy (who wrote the article)
-Or a vortex opened up by chance and remained open for both the old woman and Amy to experience it, but was closed when she went down with her husband, and all they saw was how the basement existed in their (ours) time-line.
Fascinating stuff. It's too bad that we live in a world where such experiences are scoffed away or are only found on paranormal sites with no significance attached to it.
Sometimes, Science is so shallow.