Forget about the bloody gods and listen to what I’m telling you. Cersei understands the consequences of her absence and she is absent anyway, which means she does not intend to suffer those consequences. The trial can wait. We all need to leave.
You wake up in Ceresi's body the day after the Purple Wedding. What do you do?
The big problem is waking up right then, would I still have Cersei’s neuroses as well? Her grief at losing Joffrey, her paranoia at the valonqar prophecy, her fear of being ousted from power by the Tyrells and then by Kevan, these are central driving components behind her actions following the Purple Wedding. Similarly, waking up at that specific point means that there’s no reconciliation with Tyrion (even if that were ever possible, you can’t come back from pinning regicide on him) and no putting the screws to Littlefinger for his betrayal.
If I don’t, I’m essentially an entirely new character, and my goal would be the maintenance of Lannister power. I’d patch up the trapdoor that leads to the Tower of the Hand, get Gregor Clegane to mash Varys’s face like a grape, and find something to pin on the Martells to get Myrcella back. Obviously, keeping Tywin alive is necessary, he has the requisite intimidation factor that Cersei doesn’t.
When boys and girls live in the same home, awkward situations can arise. Sometimes, I’ve heard, even brothers and sisters develop certain affections. And when those affections become common knowledge, well, that is an awkward situation indeed, especially in a prominent family. But prominent families often forget a simple truth, I’ve found. And which truth is that?
You’re a prince of Dorne. A legendary fighter. A brilliant man feared throughout Westeros. But you could not save your sister. I’m a Lannister. Queen for nineteen years. Daughter of the most powerful man alive. But I could not save my son. What good is power if you cannot protect the ones you love? We can avenge them.