Which one's the mother, which one's the daughter?

I introduced myself to one of my neighbors yesterday. Her name is Nancy. She's lived in my building for 16 years. She's the mother of six and grandmother of seven. She retired from working in personnel at MIT and now teaches ESL. After chatting for a few minutes she said, "Tell me your name again." When I said "Ellen", she said, "Oh, I won't forget your name; one of my daughters is named Ellen." Then I said, "I won't forget your name; my mother's name is Nancy!"