(Example, in a description of a room this object would instantly place you on the map, and maybe give a clue to the date, even if very roughly.)
So far she has come up with "caganer" in Spain and "pajaki" in Poland. (If you have something to say about them, please do!)
Preferably, something that is still in use, but if you know of something your grandparents did that has since died out, that could be helpful too. If you know of a good resource (like a book, an article, or a web page), that could be helpful too. (She has access to many journals through the university library - if she only knew where to go look.)
Google searches tried: Christmas, + decorations, + traditions, + European, + Eastern-European, + Poland etc.
Similar key words in Wikipedia.
Some library searches, mostly getting arts and crafts hits