The twist is that she’s been capable of this the whole time and we haven’t noticed.
“I will crucify the masters,” Daenerys says, “I will set their fleets afire, kill every last one of their soldiers, and return their cities to the dirt. That is my plan.”
“This is entirely different.”
“You’re talking about destroying cities. It’s not entirely different.”
Her arc: being torn between winning the throne through love or fear.