By her saying 'no', it gave the civil rights movement in the US a focal point. During the subsequent months (actually over a year that the bus boycott lasted), Martin Luther King Jr came into the spotlight as the leader of the civil rights movement here. Rosa Parks, with her single act of defiance against the status quo was the spark that the movement needed.
Let's remember her just as we celebrate the lives of our fallen heroes here.
--- Tontoni