When King's Landing falls, it isn't to Stannis Baratheon or Daenerys Targaryen or Aegon Targaryen. It is to Arya Stark Targaryen, the widowed wife of Aegon and mother of his newborn heir.
Dowager Queen Cersei dies by her own hand in the Throne room rather than await a fair trial that Arya would have given her. No matter Arya's hatred of the Mad Queen, she was a Stark born and bred and no number of years could change the morals that her father had instilled in her while she was still a child. Oh, she admitted her morals had slipped somewhat during the war(s) but they came back the moment she won the war and secured the throne to her son.
King Tommen died in the middle of the battle. Not early enough to save both sides from loses but still early enough to save some of the defenders of King's Landing. Arya could still remember the boy he had been, sweet and kind and in love with his kittens. Had he been more independent he would have made a good king but the Dowager Queen Cersei and Queen Margaery controlled his every action.
Queen Margaery has been with the ladies of the court, hidden deep in the Red Keep and Arya has some of what were originally Daenerys' Dothraki to go guard them until tomorrow when Arya would be rested enough to sort them out. Some of them could be political prisoners, like Sansa, sweet, innocent, gentle Sansa, had been after their father's death, others could be Lannister bannermen's wives whom Tyrion would know better.
Arya has someone remove Cersei's corpse from the throne room and orders it not to be attended by the silent sisters. She orders it to be fed to Rhaegal, the dragon that had bonded with her, like Nymeria had. Rhaegal is much bigger than the bones in Red Keep's cellars and leaves no evidence of the Mad Queen for the rest of the world but the consequences of her actions.
Someone brings Eddard Targaryen to her and she looks at her son. He has her hair and face but Aegon's violet eyes. She hopes he will have his grandfather's honor, grandmother's caring, his uncle Robb's playfulness, his uncle Jon's understanding, his aunt Sansa's way with words, his uncle Bran's cleverness and his uncle Rickon's untamable wildness. She fervently hopes that he doesn't get his great-grandfather's madness. She hopes the coin the Gods flipped landed on the sane side rather than the insane.
She never thought she'd find herself in this situation. Sansa was always better Queen material than her. Sansa was always more beautiful than her, more ladylike than her. Hell, her direwolf had been named Lady for Gods' sake while her own had been named after the warrior Queen Nymeria. Sansa was also always talking about marriage and children and being a wife. Arya thinks she would have made a better mother than Arya does and yet she's the one holding the small crown prince to her teat, sitting on the Iron Throne in Red Keep, the blood of her enemies smearing her clothes.
When little Ned has had enough, he smiles up to the only parent he will ever know and she smiles right back.
Later she will avenge Robb and mother by taking Roose and Ramsey Bolton's heads as well as every Frey's she comes across and she might even put Theon Greyjoy out of his misery despite what he did to Bran and Rickon but for now she is content to sit where she is and watch her son sleep.