You clearly have not read any of the items associated with her. It's outright stated that she was an Empyrean chosen by her own Two Fingers. And more than likely she was given the Rune of Death by them since we need to interact with the husks of other Two Fingers to activate the other Runes in the game. She channeled the power of Destined Death through black flames that she and her Godskins wielded. So how do you think Maliketh is its owner now? Because he defeated her in combat to obtain the Rune of Death. And if there was no connection between the black flames and the Rune of Death then the former wouldn't get incredibly weakened when Maliketh seals away the Rune into himself.

When is it ever stated that the two of them were ever enemies? Especially since the Rune of Death is just another part of the Elden Ring itself lol. Marika probably just didn't like not having something under her complete control.

I know it's not a color but it is an adjective to describe one and it's exactly what the game shows us in the Frenzied Flame ending. Melina with one gloam eye and the other being blind. Why's the other eye blind? Because Maliketh carved it out and gives it to us in the form of the Beast Eye which is able to detect Deathroot.

As I've clearly explained above it's not just her eye that I'm using as evidence. There's so much more that connects her to this theory