This proves the old adage: Never say NEVER. It's her opinion but it doesn't mean it's written in stone or is a Rule of Law. I've used poly and in fact, when I first began quiltmaking, a low loft poly was recommended for beginner quilters. Nothing wrong with it, and especially nothing wrong with it in dog and cat beds and crate pads.
You'll run across this 'NEVER' rule again and again before you gain enough experience to disregard it. But you will gain that experience and then those who use the word won't upset you!
Congratulations on joining the sewing/quilting community!