Board Thread:Show-Related Questions and Answers/@comment-30851494-20161226024641/@comment-25375217-20161226031905

Their memories were only erased starting from the point that they entered Camelot (as proven by them remarking as they wake up in Granny's in 5x01 that last thing they remember is heading to Camelot). Merida's interactions with Emma happened over the two days before this.