I never understood this, but isn't Medusa the tragic one? I mean she gets made into this only because she is born extremely beautiful and some random goddess was jealous of her? Sounds extremely unfair. Or was she somehow of bad character?
Depending on the telling, Poseidon/Neptune had sex with her in a temple dedicated to Athena/Minerva, and the latter transformed her as punishment. Then she may have just been chilling until Perseus came along to behead her for an unrelated situation.
That's not really how these stories went, at least for the ones involving mortals. The gods used favored mortals or demigod children as proxies instead. So maybe you could interpret Athena turning one of Poseidon's lovers into a hideous creature as her way of punishing him.
