I've had a reasonably similar problem with my friends recently in that one of them inparticular wanted to prove a point and I think that's what your sister is doing. It looks like she desperately wants you book a caesarean so that she can go around saying that you've chosen the easy option and therefore belittling you in some way.

It sounds like she's a difficult person to deal with so I'm not sure there's ANYTHING you can do to get her to shut it. You could try something simple and direct like, "Please stop talking about the caesarean, it's my decision and I don't need input from you," but I don't think she'd necessarily respect your wishes. So I'd probably just say, "no, I haven't and I'm not going to - I'm going to see how things go."

Grrrrrrrrrrrrr ... people.