I rewatched all of Daenerys's scenes in the last week, and I was struck not by her repeating "I will take what is mine with fire and blood" (which she only really said once by the way), but by how every single time she was confronted with a difficult choice, she tried to do what was right — even at great personal cost.
The show may have been building to this the whole time, but they haven't done an effective job of developing Daenerys's downfall at all. It makes no sense that she would torch all of King's Landing after the Lannisters had surrendered. Even if she is "mad" with grief, why would she attack the whole city, and not just go after Cersei? Nothing in Daenerys's character arc — nothing — suggests she would kill hundreds of thousands of innocent people rather than going straight for her true enemy.