"Queen you shall be... until there comes another, younger and more beautiful, to cast you down and take all that you hold dear"
Well Cersei's hell bent on proving Margaery's her prophesied queen, which means she's ignoring other possibilities.
I didn't add Myrcella because, she might possibly become queen but she has been mutilated severely so there's no way she's more beautiful than Cersei and also "gold their shrouds" which means she'll die before her mother. If she was the prophesied queen shouldn't she surpass Cersei?
My main theory is Sansa
She has a long personal history with Cersei compared to others in the story, Sansa has been her victim, and someone Cersei can vent on, Joffery and Jamie have been removed from Cersei directly or indirectly through Sansa. It would be an epic twist if the child Cersei mocked, abused and sneered at turned out to be her deadliest foe
Who knows maybe she's right for once
Margaery was the reason for why Joffrey was killed, and she is taking Tommen and power away from her
She was indirectly responsible for Joffrey's death
And she's taking Tommen away from her, by being nice to him
So I don't see how it could be anyone else. No oneexcpet Margaery and Sansa have taken someone Cersei holds dear
But the only way Margaery can fully destroy Cersei is by saying her children are bastards form Cersei and Jaime's incestuous fornication. But then she wouldn't be queen
Then there's Arianne. Lord knows how; either she marries Aegon (but I do want Sansa to) or Dorne becomes independent. It would be fulfilling destiny where she takes the place as queen; something that belonged to Elia
That's why I prefer her over Dany, she has more reasoning which is directly towards Cersei and the Lannisters.
It would be meaningless to both of them
all of Cersei's mistakes and failures will mount to nothing. She won't realise how incompetent she actually is; so I don't want it to be her. Also she never took anything Cersei holds dear