Holika appears in the Puranic narrative for a single scene, and the scene only makes sense inside the longer story it belongs to. Her brother Hiranyakashipu has obtained a boon of near invulnerability, and his own son Prahlada refuses to accept him in place of Vishnu. The attempts on the boy's life escalate: poison, elephants, weapons, serpents, and at last the fire in his aunt's lap. Each fails, and the failures establish that the child is protected by something the king's power cannot reach.
The sequence closes with the boon itself turned inside out. Hiranyakashipu had asked to be killed by neither man nor beast, indoors nor outdoors, by day nor by night, on the ground nor in the air, and by no weapon. Vishnu appears as Narasimha, neither man nor lion, at twilight, on a threshold, with the king across his lap, and kills him with claws. The fourth avatar of Vishnu exists to answer this one over precise contract.
Holika is therefore not the antagonist of the story but a failed instrument in it, and the tradition treats her accordingly. The devotional reading, in the Bhagavata Purana above all, is about Prahlada: what is celebrated is the endurance of a child's devotion against a father with absolute power, not the death of a woman in a fire. That is why the day after the burning is a festival of play and coloured powder rather than of vengeance, and why the story survives in retelling long after the theological point about boons has stopped being the reason anyone repeats it.