So I thought of this bc I'm writing about TWAU for a paper
The fact that Nerissa is The Little Mermaid is honestly brilliant because in the Little Mermaid the mermaid trades her tail for legs, and loses the ability to talk. In TWAU, Nerissa trades her tail for legs, and we learn that she plants "Faith's" head so her voice can be heard, because otherwise no one would listen to or believe her.
(works the other way if Nerisa is the one who died, because then her voice is never heard)
It's not just "the little mermaid is a prostitute because dark adult twist on fairytales lol", it's done to draw a parallel to how the disenfranchised, especially sex workers, are ignored by government/the elite and their voices are rarely heard.