Just to clear it up, Noel's 5D is full body invincibility, so it doesn't really matter where the attack lands on her. I'm guess the reason 5B keeps hitting through it is that 5D has a relatively slow invincibility start up (6-7 frames, have to check for exactness), so if the Noel doesn't predict/time it exactly right, they'll still get hit.
It's her 4D that's only upper-body, for future reference.
/edited cause I suck at spelling