For some people (myself included) the disappointment doesn't disappear when you get to hold your bub - particularly when it is 2 hours after they arrive. Keep giving her support and let her talk it out if she wants.

Hope it went well and that her beautiful baby has arrived safe and sound!.
I agree. The worst thing you can say to someone who didn't want a caesarean is that it doesn't matter in the end because they've got a healthy baby.

It's so, so important that she be allowed to feel whatever she feels about her little girl's birth and that no one tries to minimise it, or make her feel better by saying things like that. The most supportive thing you can say is actually nothing - let her talk.

Congrats on your little niece!