Daenerys is officially done with the "clever plans." In "The Spoils of War," the Mother of Dragons fought back against House Lannister by riding into battle with Drogon and the Dorthraki. They successfully decimated the Lannister troops and even left Jaime's life hanging in the balance. So how will Cersei react to Daenerys' attack on Game of Thrones? She definitely won't be happy, that's for sure.
After taking out three of Daenerys' allies, Cersei may have gotten a little cocky, but she had every right to be. She was winning the war. Not only did she take out Daenerys' allies, but she also got the gold she needed to repay her debts to the Iron Bank. Moreover, she was also shown a weapon that would, in theory, take out Daenerys' greatest asset: her dragons. But even though that weapon was able to hit Drogon, it didn't stop the fierce dragon from proceed to blow the device up.
Dany's attack will certainly alter Cersei's plans. It's now clear that taking out these dragons won't be easy. Though the large spear shooter was briefly successful, it still wasn't enough to take out Drogon, and Daenerys was able to do substantial damage with only one of her dragons. She still has two more, and Cersei now knows they shouldn't be underestimated.
Moreover, Cersei will probably be extremely angry when she learns Jaime is either dead or in grave danger. For Cersei, Jaime is the only family she has left and also the only person she actually loves. While she didn't seem to be moved by the death of her son, Tommen, last season, one has to believe that she'd feel something if Jaime was hurt in any way.
Even if she isn't saddened by it, she'll definitely be even more angry with Daenerys if Jaime does die or ends up being her prisoner. The last time Cersei was truly upset, she blew up the Great Sept, so one can only imagine what she'll do now.
One theory is she'll somehow get her hands on a dragon horn. This mystical horn will give the user the power to control dragons — something that would definitely give Cersei the upper-hand once again. Though there's been no mention of a horn on the show yet, in the books it was Euron Greyjoy who found a horn. In the books, he actually pursued Daenerys and gave the horn to his brother, Victarion, when he went to meet Daenerys in Meereen. Victarion does not exist on the show, however, so it's difficult to say how this storyline will (or won't) play out.
Still, it's possible Euron has a horn in the show and just hasn't mentioned it to Cersei for some reason. Possibly so he still has something she wants in the future, in case she tries to back out of marrying him. Either way, if Euron does have it and he gives it to Cersei, that would definitely turn the tides of this war... again.