It’s not a parabola — the curve is called an “astroid”. :-D
Steve Byrnes

Thanks for the head’s up! I should have guessed that the arts-and-crafts websites were using the term “parabola” loosely. I just looked up astroid and learned a bunch of new terms.

Now that I’m reading up on this, I should mention that a cardioid is an epicycloid with one cusp. So my cardioid drawing app is really an epicycloid drawing app, and you can draw different types of epicycloids by varying the number of cusps (not lobes). Math is pretty cool! :)

Also, my niece didn’t call the curve a “parabola”. I called it that after seeing the term used by a few websites and blog posts dedicated to curve stitching. That was my error, not her’s.