Do you believe Drogon burnt that girl in ASOS or that it was a ploy by the Sons of the Harpy, Great/Wise Masters, &/or The Green Grace to get Dany to lock her dragons away so that they could molest Meereen uncontested by Dragon fire?
Regarding a potential ploy, the book answers this for you:
Her name had been Hazzea. She was four years old. Unless her father lied. He might have lied. No one had seen the dragon but him. His proof was burned bones, but burned bones proved nothing. He might have killed the little girl himself, and burned her afterward. He would not have been the first father to dispose of an unwanted girl child, the Shavepate claimed. The Sons of the Harpy might have done it, and made it look like dragon’s work to make the city hate me. Dany wanted to believe that… but if that was so, why had Hazzea’s father waited until the audience hall was almost empty to come forward? If his purpose had been to inflame the Meereenese against her, he would have told his tale when the hall was full of ears to hear.
–ADWD, Daenerys II
Furthermore, we’ve seen in historical stories like the Dance of the Dragons that dragons have very little regard for human life and will kill and eat people as well as animals, especially if the people are in between them and their food, especially if the dragons are wild.
Even for a son of House Targaryen, there are always dangers in approaching a strange dragon, particularly an old, bad-tempered dragon who has recently lost her rider. His father and mother would never allow him to go near Vhagar, Aemond knew. […] Later he would say that he was so afraid of being caught that he forgot to be frightened of being burned to death and eaten.
–The Rogue Prince
Sixteen men lost their lives during an attempt to become dragonriders. Three times that number were burned or maimed. Steffon Darklyn was burned to death whilst attempting to mount the dragon Seasmoke. Lord Gormon Massey suffered the same fate when approaching Vermithor. A man called Silver Denys, whose hair and eyes lent credence to his claim to be a bastard son of King Maegor the Cruel, had an arm torn off by Sheepstealer. As his sons struggled to staunch the wound, the Cannibal descended on them, drove off Sheepstealer, and devoured father and sons alike.
–The Princess and the Queen
The smell of blood roused the dragon, who sniffed at Her Grace, then bathed her in a blast of flame, so suddenly that Ser Alfred’s cloak caught fire as he leapt away. Rhaenyra Targaryen had time to raise her head toward the sky and shriek out one last curse upon her half brother before Sunfyre’s jaws closed round her, tearing off her arm and shoulder. The golden dragon devoured the queen in six bites, leaving only her left leg below the shin “for the Stranger.”
–The Princess and the Queen
And considering what Drogon did, later:
Barsena’s blade was running red, but the boar soon stopped. He is smarter than a bull, Dany realized. He will not charge again. Barsena came to the same realization. Shouting, she edged closer to the boar, tossing her knife from hand to hand. When the beast backed away, she cursed and slashed at his snout, trying to provoke him … and succeeding. This time her leap came an instant too late, and a tusk ripped her left leg open from knee to crotch.
A moan went up from thirty thousand throats. Clutching at her torn leg, Barsena dropped her knife and tried to hobble off, but before she had gone two feet the boar was on her once again. Dany turned her face away. […]
Above them all the dragon turned, dark against the sun. His scales were black, his eyes and horns and spinal plates blood red. Ever the largest of her three, in the wild Drogon had grown larger still. His wings stretched twenty feet from tip to tip, black as jet. He flapped them once as he swept back above the sands, and the sound was like a clap of thunder. The boar raised his head, snorting… and flame engulfed him, black fire shot with red. Dany felt the wash of heat thirty feet away. The beast’s dying scream sounded almost human. Drogon landed on the carcass and sank his claws into the smoking flesh. As he began to feed, he made no distinction between Barsena and the boar.
“Oh, gods,” moaned Reznak, “he’s eating her!” The seneschal covered his mouth.
–ADWD, Daenerys IX
…I have no doubt whatsoever about the circumstances of Hazzea’s death.
Sorry to say, but Drogon eats people. Also, please remember that GRRM feels that his main theme is “the human heart in conflict with itself”. What makes more sense with that theme, turning out to be completely justified and blameless with all your sins merely a conspiracy of your enemies, or
realizing that your “children” are monsters and having to deal with the consequences?