[ ....Hooooh boy. She takes a breath, but it's a patient one. ] It's round. [ She repeats.

Hm... ] Have you ever witnessed a lunar eclipse? The shadow the earth creates on the moon is rounded. It isn't a rectangle or square or some other shape. Another bit of evidence is that you can see farther from when you're up higher, because you'd be looking over the curve. If the world was flat, height wouldn't matter.

[ Does she need to cite more evidence... ]