Halloween

My granddaughter, as I mentioned before, is writing a book. My husband read the chapters she has written and was amazed at the subject matter:  Denmark, children fleeing from the Nazis, Jews hiding their Star of David pendants...
Where in the world did she come across this information? 
She reads books from the OBOB list.
https://www.oregonbattleofthebooks.org/2019-2020-obob-book-titles/