Good for her, Oldden. When you mentioned carboard cutouts for the keys, it took me back to my first year with our Lowrey Holiday organ. It came with those. The year was 1960. I was 7 and it was the first year I played organ.
Most of the traditional Christmas songs are in the public domain now. You should be able to find simple scores online for free. It's also good that Stijn sent you a PM. He is a wealth of information, which I have recently discovered 😊.