In the movie after Benjamin Martin (Mel) does the prisoner exchange with Cornwallis using fake Redcoats, Tavington decides to go after Benjamin's family to get him back. When Aunt Charlotte sees the army coming to get her and the children she goes to gather the kids up and hide them. She scoops Susan up from her bed but says, "Come Margaret", Margaret is the other niece. Even if she was that panicked she would still know how to tell her nieces apart.