How is cersei intending to defend against three dragons

I don't think she has a plan beyond bringing Urine Greyjoy onto the team, and I suspect she hasn't devoted much thought to the problem. She's so consumed with hatred for Tyrion, Sansa, the Martells and the Tyrells and the smallfolk of King's Landing and everyone else who's ever crossed her... she doesn't have that many fucks left to give.

And anyway, it's not the monarch's responsibility to come up with strategies, it's her generals' and admirals', and General Jamie seems to realize that the jig is almost up.

She has no plan. She is dumb. The writers adore the character though so she will be given a magic dragon whistle that allows her to take control of dragons.

»It kind of makes cersei seem very DUMB which they have spent a lot of time trying to make her seem cunning.«

Did they?
They made Tywin say: »I don't distrust you because you're a woman. I distrust you because you're not as smart as you think you are.«
And I have seen no indication that Tywin was wrong there. And when Jamie said: »We're surrounded by eniemies (…) I'm not sure you understand how much danger we're in«, he was (unknowingly, of course) more or less echoing the words of Olenna: »[Tywin] was no fool. He understood that sometimes we must work with our rivals rather than destroy them«.
Both of them implied that Cersei was or is acting foolishly.

Well, maybe Tywin, Olenna and Jamie were wrong. Maybe not.
The thing that I’m actually trying to say is that the writers did introduce the idea that Cersei might not be that smart after all.

And in my eyes, none of Cersei’s moves were driven by smartness but by an outrageous hunger for revenge. I wouldn’t be surprised at all if at some point, Cersei’s saying: »Burn them all!«
… which would make a great scene, especially if Jamie’s around.


As for the dragons… well, it has been said in a different thread already: Probably Cersei doesn’t even believe that those stories are true or that they are greatly exaggerated, with the dragons in fact being about dog-sized like the last dragons the Targaryens had.


Edit:
One more thing just came to my mind:
When Joffrey was killed, Cersei didn’t even try to find out who killed him. To her, it was Tyrion and obviously, it never crossed her mind that someone else could be behind this. That’s pretty dumb, too, because it allows the real killer(s) to run free.