Where does SAM come up with the idea that the Native Americans [...]
As far as I can tell, S.A.M.'s ideas about Native Americans (and many other aspects of America besides) are mostly extrapolations/projections of her ideas about other issues (European colonialism, the Israeli/Palestinian conflict, the Holocaust, Apartheid, etc.). Note that she rarely addresses the subject on its own terms, rather than as a rhetorical bludgeon when discussing one of her pet issues (like in this thread).
Predictably, this makes for something of a muddle.