You can try and put this site in Google Translate. It talks about music after the war. But this is specifically related to the war. https://www.nporadio2.nl/nieuws/npo-radio-2/aa59b98d-3be2-43c7-8124-4be291f410b4/welke-muziek-klonk-in-nederland-tijdens-de-bevrijding
Songs mentioned in the article:
https://youtu.be/xawvpIgZ7Fs?si=isADm6yNrJgWcswr
https://youtu.be/8Lvcr3bi3cg?si=bJvKUhp2-AVMK4wZ
If your grandma lived close to the Dutch border its most likely they listened a lot of German radio of they even had a radio.
I can probably look for more but I don't have time now. Hope it helps.
I mostly read on other Lemmy's or however you say that. But I still come across this post. :)