Melody, u asked the right person to tell u
TR Mining The Facts Time!!!!
the most acceptable reason why Athena turned Medusa into the monster is because
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(warning: explanation for medusas hair would require TR to go inappropriate mayhem, and the explanation is related to a usually unacceptable practice, in which it may offend certain people, and will he inappropriate, proceed at ur own risk, IF YOU DONT WANT TO READ ANYTHING INAPPROPRIATE OR OFFENSIVE, I SUGGEST STOP READING THIS NOW):
So, if ur like me who paid any attention to Greek history, you'll know that Athena and Poseidon have enormous rivalries, and most of the time they completely hate each other (however, this has nothing to do with Annabeth and Percy in the Percy Jackson book series)
Athena and Poseidon will do anything they can to win over one another
Medusa was known to be highly pretty (more pretty than Mitsuko from Battle Royale), and very attractive, so one day, Poseidon raрed Medusa in Athena's temple
most likely the reason Athena was mad when she found out is that the raрe took place at her temple, and if u were Athena, you wouldn't want ANYONE to trespass your property, especially if that person u don't trust, right?
as u can see, Poseidon and Medusa trespassed her temple
Athena can't punish Poseidon, cuz Poseidons a god, and can simply get out of it
but Medusa isn't, and can live in complete danger
well, that's how the careless 12 Olympian Gods and Goddesses are, but Athena got mad anyways and punished Medusa by turning her hair into snakes, and this punishment was enough....for now....now ruining Medusas beauty forever
later on Athena would send Perseus to k**l Medusa
so, there u go, melody,that's why and how the beautiful Medusa became the girl with snake hair
youre welcome