natiels

For what it's worth I agree with the OP on the point that in this book Wayne was more vulgar than in either of the other two books. I didnt feel like it was out of character or such an increase that it seemed abnormal or "too vulgar", but i definitely noticed it.

Kaladin jumping into the arena to save Adolin. "Honor is dead. But I'll see what I can do."

I think this is on the right track. Here is my theory. Quote from the book here on page 240 (i am on the ebook so its hard to tell, it might be back or forward a page) Maybe this line was just to express Prof's annoyance and show how his attitude was being changed by using his powers, but I think it might be a clue to his weakness. Crying children could definitely be part of his nightmares if he was at the school when it happened.

Shartplate

I guess I'll answer my own question. I see that it is confirmed that vasher killed her with nightblood in the annotation here. http://brandonsanderson.com/annotation-warbreaker-chapter-fifty-six/

Do we know that he used Nightblood to slay her? I would also doubt Nightblood's ability to not kill somebody no matter how much it liked that person, but I was wondering if this is actually confirmed or if it was possible Zahel just killed her via some other means (not with nightblood).