Cersei has to die at the hands of one of her younger brothers.
Apart from enormous dragons and undead zombies, it's obvious that Cersei's biggest fear is Maggy's prophecy; especially because because it has so far played out exactly as the witch predicted.
For Game of Thrones addicts, prophecies are everything - they determine which characters we root for, how we predict future storylines, and which plot theories we actually believe.
In addition to this, Maggy had prophesied the eventual takeover of Cersei's position as Queen by a younger and more handsome candidate. It is, the True name of Jon is Aegon Targaryen, which is just the identical name of the first ever Dragon King, who almost 300 years ago united the Seven Kingdoms together.
Clapton said she knew Cersei was lying about pledging her forces to Jon and Daenerys, and this was conveyed through the dress. They will also fight for the Iron Throne on which Cersei now sits. It took time to hsoot season 7 as the makers were waiting for the favourable climate to shoot the season and the shoe kick-started from July 16. So, what is left for Cersei to fight for? After suffering the loss of all three of her children (and going through miscarriages before that), she has clearly pinned every last hope on her fetus. So, of course, it still has Euron Greyjoy who is now on his way to Essos to bring the Golden Company back, but can he truly trust him?
Unknown to everyone that was watching at the time, he was just about to cryptically reveal that Jon Snow and his aunt Daenerys were about to start an incestuous relationship (1:30 onwards).
The dress is created to look like chainmail, implying that Cersei feels the need to armor herself while meeting with her political opponents, and features a slashed pattern on the back of the monarch's fitted coat, reminiscent of a scorpion's tail. Taking that suspense away this season has reduced the show to its spectacle and lore alone. Let me know in the comments.