Cersei Lannister, the First of Her Name, Queen of the Andals and the First Men, Protector of the Seven Kingdoms, is totally screwed come Season 7 of Game of Thrones.
After blowing up the Sept of Baelor in the sixth season-ender, she has no allies left. Hightower is against her. The religious sect of Westeros — what's left of it, anyway — is against her. As she says herself in the Season 7 trailer, she has enemies to the North (Jon Snow and company), the South (Dorne), the West (Euron and the Iron Islands), and most prominently, the East (Daenerys Targaryen and her army of Unsullied). The only three people she has on her side are Jaime, Qyburn, and the Mountain.
As fearsome as the Mountain is, he's still only one zombie-man — and Dany has a dragon the size of a Boeing 747. She also has Cersei's brother Tyrion as her head counsel, and as we know, he has the capacity to outsmart his dear sister.
"Dany in Westeros makes Game of Thrones a new show," co-executive producer Bryan Cogman told EW. "It has this amazing ripple effect throughout every storyline that's very exciting to explore. There's a pace and urgency that's very palpable. This is the end game."
That "pace and urgency" Cogman refers to is seen in the newly released trailer, as Daenerys's army of Unsullied soldiers and Dothraki horse-mounted warriors storm what appears to be Casterly Rock, the Lannisters' ancestral home. (Oddly enough, we have yet to see the oft-discussed Casterly Rock on the HBO series, so its appearance in the penultimate season would seem appropriate.) With a battle between the Lannisters and the Targaryens fast approaching, what chance does Cersei have in defeating Dany and her army?
To be honest, not much. Cersei has isolated House Lannister, and with just the King's Landing military forces at her disposal, it's unlikely she's going to be able to defeat Dany at Casterly Rock. She could use her spy network to get the jump on Dany's plans, and if she has extra wildfire (it's unclear if she used all of it to take out the High Sparrow), she might be able to do some damage. But Daenerys still has three dragons on her side.
Not to mention, the trailer also shows Tyrion knocking over a Lannister marker, a lion, which seems to signify Cersei's defeat.
However, that doesn't mean Cersei is going to give up King's Landing, and the Iron Throne, so easily. In fact, she'll probably burn it all down before she lets Daenerys take it. Of course this would lead to a terrible case of déjà vu for Jaime Lannister, a.k.a. the Kingslayer, who already had to kill one Mad King to keep the city safe.