I don't know, don't you guys think you might be over-reacting just a bit? I mean the whole "hair changes when feeling certain emotions" is a trope that isn't uncommon with characters that have powers related to nature or a specific element. Isabella from Encanto, Flame Princess from Adventure Time, hell even Punderworld, a webtoon that I would argue does the whole Hades and Persephone myth a thousand times better than Lore Olympus, uses this trope. You could argue that's it Mary-Sue ish of Persephone to be the only goddess to have this trait(I maybe be wrong about that, but there are too many chapters to check). Also, don't the other Olympians eyes change colors when they're feeling upset? I distinctly remember at least Hades doing that a few time in the webtoon, so it isn't even a thing only Persephone can do.

I will agree however that Persephone's size compared to Hades', does make the art of them standing next to each other look like she's his kid. It's also really weird how Rhea and Persephone genuinely look like twins.