A Medusa in DnD is a species--a monster type. There are many of them--DnD mythology is not the same as real world mythology. Medusa is NOT just one Gorgon in DnD. I quote from the ADnD Monster Manual: " Medusae are hateful humanoid creatures which dwell in dark caves or caverns, venturing forth on occasion to seek prey. They try to beguile humans to look into their eyes."
Also: WE PLAY HOMEBREW AD&D + 3.5 HYBRID.
AND THIS REGARDING TIEFLINGS. Notice the word "often" as opposed to "always". Changes the meaning of the sentence doesn't it? And yeah I have read the 3.5 Monster Manual entry for tieflings but we play homebrew so my first like nine game sessions were totally AD&D despite the fact that I was allowed a 3.5 character race. If I want my tiefling's demonic lineage to be more recent nothing is preventing me--I have a whole back story for her too. I'm not confused about tieflings and half-fiends. We may have simplified our explanation to Sasha (since she's a brand new player) for expediency's sake. So fucking sorry. (That last sentence there was sarcasm, by the way.)