[Nobody heard about Holocaust in 1942 and they wondered where did she get the idea.]
https://en.wikipedia.org/wiki/Babi_Yar
https://en.wikipedia.org/wiki/1941_Odessa_massacre
Note that there were partisans in German-held territory who would not have missed the mass graves, some of whom would probably have personally witnessed the mass killings from afar, thanks to elaborate concealment tactics combined with binoculars.
German antisemitism wasn’t an aspect of Soviet propaganda until later in war anyway. Maybe the rumors were spread but that is all.