Please recall that Sarah grew up in an Assmebly of God church, and later became involved in the Bible Church movement. These are denominational groups intensively missionary-oriented with very strong connections to Africa. The idea that she would live in that milieu and not know that Africa is a continent is like saying a religious Jewish kid didn't know where the Mediterranean was. It's simply not believable.
A little more on the missionary thing. I don’t mean “missionary” as in a pair of white-shirted guys cruising around suburbia. Most AOG and Bible churches of the period of her growing up had (many still have) world maps in the lobby showing where “their” missionaries serve.
I grew up in such a church. The giant missionary map was in the sanctuary with little blinking lights for eachof the 52 missionary families our church supported (50% of all collections went to missions, mostly overseas). I spent many a sermon studying the map on the wall.
Again, there is no way this Africa comment is factual.