She is beloved to her sisters, even in her death, and they will never forgive Athena for her death.
Their transformation had been bad enough, but they had killed enough men for the pain of that to diminish and fade over the past few years. But this was not something that could be undone, for them to be left immortal and never to reunite with little Medusa again.
Stheno and Euryale can never do anything to bring her back. Hades will not grant any favors to those who stand against Athena and can slay men with their very looks, though Persephone had visited once, bringing them what she could. But the alliances of those constrained by other goddesses could never sustain itself forever, and Persephone had made her escape as she could.
But they can do other things. They know the types that would be Athena’s favorites. Would, if they could only survive long enough to do so. Stheno is talented at finding and killing, lurking with her head veiled until she lures them away from their family and into the wilderness, where they join the legions of those lost. And Euryale bellows and bellows, distracting attention from her silent sister. Her bellows frighten those who hear them, and even Zeus on his throne wonders if Athena has sewn her own doom.
Athena trusts too much in her wisdom and skill, and the Gorgons know this. Medusa had, beneath the bitterness, still loved the goddess she had served as priestess to too much to hurt her. But they have no such love to bind them, and Stheno had always favored Ares, and Euryale, Aphrodite, and those two have no love for Athena.
Stheno worships Ares when she can, sneaking into his temples before she goes for some of her kills, and she doesn’t wonder that those kills become easier and easier over time, for she is at war against Athena’s choosen and their ends will be violent.
And Euryale seeks out men who don’t shy away at her refusal to remove her veil, but have refused her sister’s attempts to lure them away. If those men are found in bed, the people whisper that they were taken as though by sudden poison, never knowing how close they have come to knowing the truth of it.
Their revenge is not swift, but it is certain, and Athena never figures it out, for all her knowledge. She expects them to be monsters, and they are, but they are monsters that loved their sister, their baby sister with her dreams of knowledge, and they will never forgive Athena for that. Athena needs her worshippers, for she is as vain as the rest of the goddesses, even if she pretends not to be. And if they spend the rest of eternity wishing for their sister, and sneaking into men’s houses to kill them before they can begin to please Athena, they’re happy for it.
Because she took what was theirs, and they will take what is hers.