Mitch,
Welcome to you and, I hope, your mother-in-law!
I do know that Charlie sings a song to several children very early in Charlie Chan in Shanghai. He refers to Fu Manchu, which is kind of an inside joke since the actor playing Chan in that movie (Warner Oland) had played Fu Manchu in several other movies!
If you'll go to the main page of this website and click on the "Links" section, you'll find several places where you can find CC in Shanghai and all other available Chan films!
Do you think she might like to see Charlie Chan in Rio?!?!
Virginia nailed it! As shew notes, the only mention of Fu Manchu in a Charlie Chan film is, indeed, in the song, "Princess Ming Lo Fu," that Charlie Chan sings to a group of childern while aboard the ocean liner en route to Shanghai. The words to the song may be found among the information that we have for "Charlie Chan in Shanghai" located elsewhere at this site.