I don't know if it was ever said to her but it's come up on the forums before.
I don't know if it's common knowledge: I certainly didn't know it till probably college, and sinse must people aren't versed in anatomy they make the comparison to human: whatever's on the ground is the foot, the next big joint is the knee etc. Because actual knees are close to the body line, and fairly hard to discern, very different than people, they assume. And don't really care, so they don't consider it.
It shouldn't have gotten through research and editing, if I had to justify it:
As I recall, it must it wasn't described that the creature had back-bending knees (Hork-Bajir the exception, and they are written to have either way at different times). Mostly it was written that in the process of a morph, one's knees changed direction.
Well no one ever said morphing is conservative. There's not reason that knee couldn't become the animals ankle, the bones of the lower leg than becoming parts of the foot, and other bones rearranging or just being newly generated.
Personally I was always annoyed that their arms always became wings, and no one ever just lost the arms and grew wings from the back. Morphings not evolution: it doesn't HAVE to build on existing structures. Just seemed to do that alot