The marriage was never consummated, so she was never actually Joffrey's wife and doesn't inherit land or titles. And it certainly seems like, in the show, only male heirs can inherit the throne, so she wouldn't be eligible regardless. Which makes Tommen the next in line, right?
And I felt that episode was somewhat weak. I mean, yeah, OK, good ending, but I was left feeling like not a whole lot else really happened. And if an episode can kill off my least favorite character in television history and leave me slightly bored, well, I don't know. Maybe a subsequent rewatch will reveal more subtle intricacies.
Actually, now that I think about it, no Daenaerys and no Arya/Hound in that one and a whole bunch of Boltons/Theon and Bran... I don't really give two shits about those storylines, so this episode wasn't going to rate highly with me regardless.
And, yeah, MongGrel, I don't know what your intention is, but spoiling the show for us just because you know the story ahead of time basically makes you Joffrey. No one wants to be Joffrey. Knock it off.