While doing more research for ML, I found another wealth of information that the other members of her family hadn't found yet: the FULL passport application of an uncle. Sure, they had the first page, but they were missing 4 additional pages of information! How could this be?
Ancestry only indexes the first page of a passport application. This means to find the other pages, you have to use the "next page" buttons within the document viewer. This gave some incredible details including a photograph of the family.
One of the most interesting bits of information attached to the application was a translated letter from Poland describing the situation after World War I. Homes destroyed, family missing, a relative captured by Russians, etc. All this provides a backdrop to why this relative needed to go back to Poland, sell his things, and bring his mother-in-law back to America.
So, when viewing records, don't forget to check the next page! You never know what else might be attached to that first page.