Since I made this post, I've kind of modified my... theory, or whatever. Ebrietas seems to have a connection both with the Parasite, as well as with the Lumenwood flowers, and in fact, her anatomy is somewhat similar to that of the Lumenwood Hunter. Her limbs branch in unusual ways, similarly to a plant, which would fit the Kos Parasite description: "a Kos Parasite is said to stimulate phantasms inhabiting a lumenwood."
I don't mean that Ebrietas is directly the child of Kos, but that the parasites within Kos were fostered and merged with another host, likely a human, which eventually became Ebrietas. Ebrietas also bears resemblance to the Celestial Emissaries, a race of otherworldly beings whose true origin is purely terrestrial, being the completed phase of the Research Hall's ghastly cerebral experiments. In concept art, Ebrietas even sprouts the same glowing tendrils as the advanced Celestial Emissaries, and her inflated head reveals a pocked mass similar to the Brain Fluid amoebas (cont'd)