an Akata Witch question

I'm reading Akata Witch by Nnedi Okorafor, and I know some others in my circle have read it, so maybe you can help with this. I'm not sure whether this is a mistake that wasn't caught in editing, or whether I misunderstand the timeline but in chapter eight Sunny says to Orlu "But you and I have been going to the same school since we were about five." (on page 141 in my edition), but earlier we were told that Sunny only moved to Nigeria from the US when she was nine. I don't get it.