In my days of isolation, I went and watched literally every video by The Tarnished Archaeologist, which takes a rather novel approach to uncovering the lore of FromSoft games - primarily Elden Ring.
To summarize the theories he puts forth (they? I'm not sure if it's just him or a team that works on the channel, as the narrator usually refers to "we here at the Tarnished Archaeologist," but that could just be a linguistic convention) that are most relevant to this discussion, here is what we have:
First, he suggests that under Marika's rule, that people are literally born from the Erdtree - that just as they are absorbed into the Greattree roots that are (or rather were) linked to the Erdtree, that people literally blossom off of the tree like fruits. This is not the case for everyone - Boc the Seamster, our Demihuman friend, was likely born the way you and I would recognize. But the point is that TA suggests that the Erdtree is the giver of life in Marika's regime in a very literal sense. In a similar manner, it's implied that Millicent and her sisters were born as buds from the great Scarlet Aeonia in Caelid (which, unlike the ones found at the Haligtree, one next to Malenia boss chamber and one found only after we defeat her, has grown into a more complex plant-like structure) and are thus Malenia's "daughters." If the Erdtree is to Marika what the Aeonia is to Malenia, perhaps Marika's children are fruits of that tree.
Second, TA posits that the Gloam-Eyed Queen was the previous God, before Marika ascended, and ruled from Farum Azula, with Placidusax as her Elden Lord.
There are a few things to back this up. One of the issues, of course, is the timeline. It's very difficult to order the various events and causal chains. For example, was the Shattering War before or after Radagon replaced Godfrey as Elden Lord (or did that event happen around the same time)? Were the Eternal Cities ever on the surface during Marika's reign?
Melina is a key figure in the game, but one who is also shrouded in mystery. There are a few things that seem likely about her:
The first is that she's probably Marika's daughter. She says she was born in the Erdtree, and that seems to be Marika's privileged domain.
Second is that she is associated with flame. Not only does she have burns on her hands, but she is needed to burn the Erdtree as part one of our steps to get access to the inside of the tree to face Radagon.
Third, is that she tries desperately to dissuade us from taking on the Frenzied Flame, and if we do so before she burns herself (and we use the Frenzied Flame instead to burn the Erdtree) and then we do not purify ourselves with Miquella's Needle, and thus get the Lord of Frenzied Flame ending, we get a cutscene in which Melina opens her ever-closed eye to reveal one that is a kind of dusky blue as she vows to destroy us.
This dusky eye has led many to conclude that Melina is, in fact, the Gloam-Eyed Queen.
And that could be the case. But I have read some theories and considered some of the elements in TA's analysis along with other theories that suggest that perhaps there's another explanation.
So:
According to TA, and the evidence is there, Farum Azula is a city with Beast Men and Dragons. It also has funerary urns for ashes and carvings of human figures as well. We also see that the Godskin Apostles are semi-draconic in form, with the Nobles in particular getting these long reptilian tails.
The Godskins are affiliated with the Gloam-Eyed Queen. And their Blackflame is basically Death (Destined Death, or the Rune of Death) made manifest.
We fight Maliketh in Farum Azula, where he guards Destined Death. Maliketh is also a giant wolf - a beastman (not unlike Blaidd, and it appears Maliketh served a similar role to Marika). Maliketh is also, under his guise as Gurranq, someone who encourages the collection and consolidation of Deathroot, which is another manifestation of the Rune of Death.
Maliketh, being a wolf-person, might be related to the beastmen of Farum Azula.
It's said that he defeated the Gloam-Eyed Queen for Marika. And he's also known as the Death of Demigods - meaning that he likely killed many of the Gloam-Eyed Queen's progeny, if indeed she was the God of her age.
So, would it make sense for the Gloam-Eyed Queen to be Melina?
Possibly not. Melina seems to be of a generation with Miquella and Malenia, meaning that Ranni, Rykard, and Radahn are all older siblings of hers, along with Mohg and Morgott. All of these children were born after Marika ascended to godhood (at least I believe so - in theory Radagon and Renalla's children could have been born before Mohg and Morgott, but I've always thought of the Omen twins as being Marika and Godfrey's firstborn, during the Crucible era).
There is one way in which the Gloam-Eyed Queen could be Marika's daughter though, even if GEQ pre-dated her as the God and vessel of the Elden Ring. And that would be if a slain GEQ were fed into the Erdtree roots.
See, if some - perhaps specifically the demigods - are born via the Erdtree, it would make sense that this was how Melina was born. But if the Erdtree is also basically a big soul-recycler, reincarnating people after death, then it's not inconsistent that Melina could be the recycled soul of the Gloam-Eyed Queen. Marika, this god of life, getting the ultimate one-up over her erstwhile rival by making her live again now as her daughter.
There's another possible explanation, though:
One of the first things Gurranq gives us is the Beast Eye, which basically lets us know if we're near any Deathroot. The eye has a remarkably similar look to the blue eye Melina opens if we get the Lord of Frenzied Flame ending.
Thus, I've seen theories that the two eyes - one locked away by the tattoo on Melina's face and the other held by Maliketh - could actually be the eyes of the Gloam-Eyed Queen. In other words, Melina might have had this eye transplanted into her head.
This actually resolves some issues: Melina has lots of symbolic association, but aside from this eye, we don't really get much in the way of connection between her and the Godskin Apostles or other Gloam-Eyed Queen stuff.
Still, we are left with some questions:
It seems apparent that the Erdtree has burned before the game - Leyndell does have a lot of ash in it even before we unleash the rune of death (though clearly not as much) and Melina is already "burned and bodiless," meaning that she was probably involved in the burning of the tree before. Indeed, as TA points out, the Erdtree as we see it looks more like the illusory saplings at which we find Erdtree seeds than it does the Minor Erdtrees we find around the map, meaning that the giant tree (or at least all by the shard of it that seems more solid and real where the entrance is) is probably an illusion - an object of faith, rather than the very real provider of life-giving sap it once was.
The GEQ was said to have fled rather than being killed. Ranni speaks of a mentor character - Renna - who taught her some of her sorceries and also was the model for the doll her soul now inhabits. And Ranni seems to play a key role in the assault on Marika's bloodline, unleashing the Night of Black Knives. While Marika probably made a lot of enemies in her campaigns to assure the primacy of her Erdtree, is it also possible that Renna was actually the Gloam-Eyed Queen, empowering Ranni as a way to take her revenge.
There are some big questions about Marika's volition in all of this, of course. I'm of the opinion that Marika is actually urging us forward over the course of the game, as I think that the Radagon half of her (whether he was an alternate persona she created or a separate person who was merged with her) has taken control, and she's trying to break free. (Like in Bloodborne, it seems that the great horror is an attempt to control women's choices over their own bodies - Ranni slays her Empyrean flesh lest she be controlled, and Marika likely had Maliketh impale her womb with Destined Death, showing the lengths to which women can be forced to go to retain autonomy. Indeed, perhaps Godwyn's targeting in the Knight of Black Knives was because Ranni was going to be forced to marry him and make him Elden Lord - a theory TA puts forth).
Actually, just throwing this out there: Melina offers to play the role of Maiden to us, which mechanically means that she levels us up. But "Maiden" in a literal sense means virgin and - with one major exception in Christian tradition - virgins don't give birth. Melina merely "plays" the role of maiden with us. If she were, in fact, the Gloam-Eyed Queen, she would be a mother many times over, as we know that Maliketh slew a whole bunch of demigods that were the GEQ's family. (And, just to toss this at you: the Godskins might be those demigods of the prior age - their draconic features could be inherited from their father/Elden Lord Placidusax).
Man, I could keep going on here - TA suggests that all birds are descended from Dragons (not unlike how real birds are descendants of dinosaurs,) which could link the Storm Lord whom Godfrey defeated to take over Stormveil Castle might have been a dragon - maybe even the Elden Lord! That could explain the presence of the Banished Knights at Farum Azula.
See, the thing I love about these games is how utterly complex and deep the lore is, all fitting together shocking well if can find the connections. I'm tempted to attempt at timeline for Elden Ring, but that will be an arduous labor.
It'd be really cool to see the process by which FromSoft goes about actually determining all of this stuff (and how much of it is lucky coincidences, as a lot of people have speculated - though I'm of the opinion that it all works too well to actually be a mass hallucination of sense - this is the video game equivalent to the kind of novels English scholars will pore over for over a hundred years).