I find the whole Danny went bananas all of a sudden narrative odd to be honest, i think on reflection its more that people including myself didnt identify it and we are all not as clever as we think we are.
Look at her character, parents and sibling murdered, orphaned and forced to leave her home, abused by her brother, sold into marriage, sexually assaulted, husband died, lost a baby, kidnapped, betrayed by those closest to her, watched her two dragons get killed, watched her best mate be beheaded. Is it really that hard to understand that she descended into madness or prone to extreams act of violence based on simple psychology.
As the above events unfolded and accumulated, so did her acts of violence, complicit in her brothers murder, burning alive a midwife, locking some dude in a vault, burning alive a slave master, crucifying all the master in mereen, feeding one dude to her dragon, burning all the Khals to death, returning to Mereen and killing the rest of the masters in Mereen who had invaded, Killing the Lanisters at high garden, burning the Tarleys. Is it really a huge leap to killing and burning the whole of kings landing.
It actually is a very logical and noticeable escalating pathway when you break it down. I didnt notice it mind and i think because of that it was the twist of the entire series. It plays on your own concepts of good guys and bad and the moralities.
I think people think it was all of a sudden, but if they honestly reflect on it, it was logical and they just didnt identify it as clever as we all like to be about GOT, we were asleep at the wheel. It was actually very subtle, slow and nuanced over many series's - very clever.