The problem with the Sansa/Arya twist is the scene where Sansa snuck into Arya's room. If they were conspiring together, there was no reason to have a confrontation behind closed doors with nobody else in the room.
Thought it was funny when Cersei called Jamie the stupidest Lannister. Although I think Tyrion is giving him a good run for the title. How many more times can his advice be wrong before Dany changes his position to court jester?
Cersei's plan won't work. Jamie was right, whoever wins in the North will march South and wipe her out. Her only shot was one of unity, especially if she stayed behind and Jon and Dany both died in the fight with the dead. She could have then taken the position, that I'm sorry they died defending us, but we lost a lot of good men as well. I did right by the kingdom, bend the knee. Her tactic will only serve to get her wiped out.
Of course it won't because this is a show and they're not going to let Cersei win in the end. The fans of the show would hate that. The Night King will be defeated. Theon and the Hound will get their redemption even if they end up dying doing it. Cersei will be defeated. Only question is how. My guess is Jamie dies valiantly in battle. Arya takes his face and kills Cersei. The only real question is what happens between Jon and Dany. I suspect that will be addressed by her becoming pregnant.
Unity and hoping Jon and Dany die in the fighting is not a plan for victory. If Jon and Dany die, the dead most likely would have won. Letting your two enemies fight each other while you build up your forces is a good plan.
Cersei correctly surmised that one of the dragons is dead. If one dragon can die so can the others. Without the dragons, Jon and Dany's forces are very beatable. There were only 8000 Unsullied to start and at least 1000 should already be dead from fighting. Robb Stark's northern army only had 20K men and they were pretty much wiped out. The Dothraki are impressive but they aren't made for conducting sieges. If Jon and Dany defeat the dead, their forces will be significantly depleted.
Meanwhile Cersei is rebuilding her forces. 20k Gold Company mercenaries are on the way. Euron controls the seas. More ballista can be made. More wildfire can be produced. The way Qyburn was looking at the dead remains, I wouldn't be surprised if Cersei has her own dead (or half-dead) army.