This sounds like a bit of paranoia to me. Buffy Ste. Marie's "Universal Soldier" had extensive air play on stations that played folk music (there weren't that many), and even here in the States there were folk rock covers of the song. I, conservative even then, still have my original copy of her album, "It's My Way," which features 'U.S'. It's as powerful now, as it was then. BSM went from folk music, to folk/country, to acting and to a long run on PBS--Sesame Street, I think.

Did someone steal some of her recordings? I don't know. Did it matter to her career if they did? Probably not. Ideas don't go away with petty pilferage. Did Lyndon Johnson like her? Hell, he probably didn't like 99% of the folk/protest songs or singers!