That's kind of how I feel about it myself and why I keep seeing this huge disconnect between her Season 1-7 deliberate cruelty and her indiscriminate rage in The Bells. It's perfectly plausible why she went insane, and what she does after going insane is understandable knowing who she is. But the compressed nature of the show in the last two seasons just undermines the whole thing. For something this drastic, I would've preferred if it was believable as opposed to simply plausible when you dig into it. And for me this includes the moment she went insane itself. The bells are ringing, she looks at the Red Keep in the distance, and we never learn what goes through her head. GRRM will probably have her go insane in the novels as well, I think, and when her inner monologue gets written on paper, it will be much more clearer. But on TV it just looks like her mind snapped for some unknown reason and that stretches it past my suspension of disbelief.