My theory is that Noelle didn’t get fatally injured, killed, or became comatose from the thorn ring insertion in chapter 4 snowgrave. She just became full-on deranged. That’s why Carol still treats Noelle as alive. She even wants to go with Kris, a sign of her derangement towards obeying Kris as her only purpose.
Noelle pretends to be sane near Carol, but outside of that, she has become your peon.
...no? the crack was a replacement for the falling apart rose. The crack is meant to represent what the rose did, which i don't know, but it wasn't badly hurt.