"I was sure that if the tables had been turned we would have acted differently." Do you believe that? Why does Annie make this claim?
No, I don't believe that, but I absolutely see why Annie would make this claim.
This claim refers to the idea that Africans would have acted differently if they had been in a position of superior power when they encountered Europeans. If they (the Africans) had been technologically superior, and the Europeans in a state they saw as savage, Annie's saying that they would have been kinder, fairer, and in all ways better towards the Europeans. She has to believe this, because it gives her and those enslaved a sense of moral rightness—and because it holds the Europeans responsible for their actions. If any human who had the power would take slaves, because that's just the way things work, then the situation is almost excusable, which would be a crushing idea.