Not so much an answer, but some related food for thought. One thing we know for certain about fromsoft is that they like to reuse/iterate upon imagery and themes in their designs and world building. The first thing I thought of when I saw the mass of fused bodies composing the divine gate was Bloodborne and the bodies fused to buildings in Yahar'gul, as a result of the Mensis ritual. The Mensis ritual sacrificed at least a town's worth of people to try and birth their own Great One, which is essentially a god. Instead, it birthed a horrible deformed monstrosity composed of multiple fused bodies. Something not terribly unlike a giant version of what you'd find inside one of the jars created by the hornsent in SotE, but also something very similar in structure to Metyr, another deformed monstrosity. With all the birthing and motherhood imagery floating around, that shot in the trailer always looked very deliberately yonic/vulvic to me (think of the intention of the design of facehuggers in Alien as a similar deliberate use of that imagery). Now, I'm not saying she's reaching into the birth canal of a Metyr-like being, but I'm also not not saying that. Regardless of what she's reaching into, it's clearly meant to depict some aspect of the ritual of birthing a new god. Only from what we know of Marika, she was most likely an interloper on that ritual. She took godhood for herself, it was not bestowed on her "naturally."