Technically, no propaganda of any sort at all.
Counter propaganda or anti-propaganda is just differently angled propaganda. You cannot fix propaganda with more propaganda.
If you want to understand your mom, you need to see or read what she sees. Just telling her she is wrong is not going to help. Repeating that she is wrong is jot g9ing to help.
Plus as an adult that she is, you might not be able to dissuade her. Perhaps, you may have to simply not touch the topic when with her.
When I was younger, I naively used to think that if I had the facts or Academic papers or research to prove point XYZ on side l, that I would be able to argue valiantly against some people I used to know. Ha, I was so silly. I could literally point or give the proof to my arguments on a silver platter, down to page numbers or exact quotes, and people would simply not even bother to read them, because they were certain they were right. Some people just want to be Right, not Correct. Due to such worldviews being driven not by fact but by emotion. Fear, anger, bias, lies by omission, but usually peppered with some facts here and there, etc.
Trying to change them, will just end up in damaging your current bonds. Do you want to risk that? Maybe over time. But just focus mostpy on what you have and enjoy the time you have, over spending it arguing. Life is short enough as it is.
But… This is a good thing. I will take it. More FOSS awareness is great news. As long as it sticks.