I have rewatched the early seasons ten times, the later seasons a half dozen each. After "The Bells" I rewatched ALL of Dany's scenes one after another back to back --there are Youtube playlists which compile them so one can do so easily.
An important point that many fail to consider (or one which gets downplayed along with every other red flag event in her history) is that Daenerys was raised by Viserys, not Mother Teresa. There was always a dichotomy to her character: the compassionate champion of the downtrodden with whom she could empathize because she herself was under Viserys' heel for years, and the ruthless, vengeful, angry side derived from her Targaryen heritage, from the other unfortunate effect of abuse from Viserys and totally lacking a nurturing mother and father during her formative youth.
Had she possessed a mature dragon back then, she would have probably burned Qarth.
Of course, a mature dragon might have gained her a more hospitable and cooperative reception too!
When she chose to crucify the masters indiscriminately, Selmy advised against that and counseled her to "answer injustice with mercy" instead, but the ruthless side of her chose to "answer injustice with (so-called) justice" which in the Targaryen book is the Law of Retaliation (e.g. "an eye for an eye"). After Selmy was (foolishly) slain in battle with the Sons of the Harpy, she retaliated by rashly imprisoning the Mereenese nobles and intimidating them by burning/feeding one of them to her dragons:
She had a fascinated look on her face as she witnessed this execution.
Varys proved these nobles' innocence in the following season when he discovered that the Sons of the Harpy were supported by leaders outside of Mereen --whoops!
And had Tyrion not been present in Mereen, she would have used her dragons to return Yunkai, Astapor and Volantis "to the dirt" as well.
All that was required to unleash this darker side more fully was the right set of conditions --which the writers created, but they clumsily threw them all together in a rushed sequence which made the turn feel sudden and unearned to many viewers.
The solutions:
1. If Dany must intentionally burn all of King's Landing, I would have lengthened the seasons to let her dark descent "breathe" a little and/or (barring that) included additional scenes of morally-questionable judgement and behavior from her gradually and regularly throughout Seasons 7 and 8.
2. Without the above, I would have approached Season 8 differently, killing Rhaegal at King's Landing instead (perhaps from a less prominent, centrally-located scorpion just as the bells started ringing) and used this as the pivotal catalyst for her turn. After that, she would have directed her fiery ire against the Lannister soldiers
only and on the Red Keep itself (so as to fulfill the vision of the wrecked hall from the House of the Undying). The civilians that die are collateral damage from the reckless rage of her attacks. Buildings in King's Landing are set alight when she burns the soldiers in the thoroughfares and fire spreads to, and engulfs the rest of the city naturally, worsening dramatically as Aerys' hidden caches of wildfire go off too.
3. No matter what, even without the alternative approaches above, Dany needed to see some of the results of the devastation --the burnt children, feel some remorse and shed some tears as the other, more compassionate side of her nature attempts to resurface, but also some lashing out when her actions are condemned by Tyrion and Jon. I wanted to see her get upset and speak irrationally as she attempts to reconcile and justify this damage to herself and others, which better reflects the turbulent internal conflict of her dichotomous nature and the onset of madness.
Of course, all this would have been way beyond the skills (or interest) of D&D.
