www.victoriousbirth.com has a great list of things to say and what not to say. Best thing right now is to listen without offering any advice or opinion or personal experience stories. Just let her do all the talking, she'll need to talk to someone about how she's feeling. And how she feels today doesn't mean she'll feel the same way tomorrow or next week or next month, even. Tell her it's ok to feel that way, it's ok to be happy the baby is alright and it's ok to grieve the loss of the birth she thought she would have.
