I think open with something really, really positive like "what a gorgeous baby, haven't you got a clever mum" so straight off the bat she knows that you're proud of her and not in any way judging her.

Then ask her how she is. If she wants to talk about the c/s she will and if not, she won't. I wouldn't ask her about that specifically unless she starts talking about it first.

But I think ooohing and ahhhing a lot about the baby helps everyone feel comfortable.