There is also cold rage; the kind that banks internally until it builds to violent, sometimes deadly, reprisals. I won't speak for anyone else here, but I doubt I'm the only one who's seen that irl. It's not a switch - it's a fuse. I honestly had no trouble believing that Dany would just burn it all down for all of the reasons some of us have already pointed out about her Targaryen genes and her past first impulses. I thought EC did an impressive job of acting showing Dany's growing despair and anger.
My biggest objection to some of the takes on Dany's (and Grey Worm's) attack on the city and the civilians is that it was a war crime, and that Dany even understood that term. There were no war crimes; there was just war, and it was brutal, and the civilians (another modern thought) were at the mercy of whatever armed group came through. That was a recurring theme of GRRM's stories. According to current thought, ASOIAF was teeming with war criminals. Even in the show we can count Robert Baratheon, Tywin Lannister, Tyrion using wildfire during the Battle of Blackwater Bay, Walder Frey, all of the fucking Ramseys just to start the list. Dany would have committed multiple war crimes: crucifying the slave owners; incinerating all of the soldiers and animals in the supply train; incinerating the Tarleys for not bending the knee. I just don't see it as useful or relevant term to apply to Game of Thrones. What Dany did was wrong, hateful, immoral, if you like. It was made more horrifying by using her dragons as weapons. If everyone had dragons? I believe it would have been more like an established tactic.