How did she come up with that random question?
Because she knew what concupiscence was. She'd learned it from adult Bible study at church (I had her come with us instead of going to the kids class when she was in high school - yes, I'm a rebel.) She'd also learned it at home from our home catechesis.
Have you been avoiding the use of "big words?" Here's a quote of Pastor Paul McCain from the October 27th Issues, Etc. show:
I have to give credit to Pastor Peter Bender, who years ago at a seminar I attended said something that's always stuck with me. The argument we often face is we cannot teach children words they don't understand, and he said very simply, "If that was our attitude, then none of us would ever learn to speak, because the words we learn as we're learning to speak we don't understand, we just say them, and then we grow into these words." So learning the words is the foundation for understanding what they mean.