The context is that I'm an engineer and she wanted to know what I learned in engineering school, so I said calculus. (In my case, I only made it to pre-calc in highschool.) I swear I'm not the type of parent to try and push this stuff on her. I said it's about understanding how things change and then I tried to illustrate it. I'm open to suggestions on how I could answer her better.
“Calculus is the horror that revolutionizes the way you perceive problems involving rates of change and you will wonder how you got along without it for so long if you put it off.”