Thank you, I already have got a copy of Stern's 1935 monography.
In it, Stern proves, based on archival material, that Luise Grafemus was never a soldier. However, her husband seems to have been indeed a Wachtmeister. Of course, she never received the iron cross.
Luise Grafemus' story about her exploits varied form place to place where she told her story (but this may have been the fault of those who wrote it down).