If she really grew up in Waterloo, then I don’t see how she could possibly have made this mistake. Unless she had no interest in John Wayne until he became a convenient political symbol.
I think she just blew her theme right out of the water in Waterloo.
You see, she was hawking John Wayne as a central theme. John Wayne’s America.
http://www.newsmax.com/InsideCover/bachmann-newsmax-interview-romney/2011/06/26/id/401507
She moved at age 12...it’s quite likely a 12 year old girl didn’t care much about John Wayne in ~1978.