Originally Posted by Harry's polo shirt
She is probably smiling so much, to make everyone calm down about her hospital visit. She wants to put a front of being healthy and fine, she doesn't want to alarm anyone.
And she is probably laughing to herself, maybe she was a little embrassed about the fuss etc. I think she and Felipe looked like any normal first time parents-to-be and I sure many others around the World leave hospital after a flase alarm only we hear nothing of them as they are neither famous nor Royal.
I was actually quite happy that they left via the main door and did not try and sneak of and make it in to a drama.