i will say, of all possible interpretations i've heard and made over the years regarding Melina, and just where she got her burn scars, the one that feels the closest to canon to me is that marika asked her to burn the shadow of the erdtree
i think the queen, especially early on when the erdtree was flourishing and fundamentalism hadn't developed yet, would have regarded the twisted parody of the holy tree, and truly what it represents as the sum of the notions rejected by the golden order, as utterly abhorrent
at the same time, melina had visions of the erdtree burning, so similarly to how marika caught two birds with one stone by using messmer as leader of the crusade + getting him away from the erdtree (such that even if he transformed into a giant grace-eating snake it wouldn't have been an issue), i can see how she would have tried to finagle the prophecy by making melina burn the not-quite-erdtree. not even getting into how melina as a child of marika and radagon would have had empyrean flesh before burning it down.
