I noticed when looking at the wikipedia page for Season 3 of GoT, that Shireen and her mother (who's name is escaping me ATM) are new characters. So does that mean that they skipped over the prolouge from ACoK?
Selyse was mentioned a few times in S2, but we hadn't heard anything about Shireen.
In fact, one theory being presented is that since there hasn't been any casting for Edric Storm, they might change the plot of Melisandre wanting to sacrifice him into her trying to get Stannis to sacrifice Shireen to the Red God instead.
Of course, this will make Stannis not holding it against Davos for stopping the sacrifice a lot more reasonable.