If Norah Everhart is descended from the Naacal then why is she mortal?

In Call of the Sea, Chapter 5, one of the ichor pools shows a vision that clearly states that all Naacal have now achieved eternal life.

The Norahnomicon viewable in Chapter 4 (and the rest of the storyline) seems to make it clear that Norah is descended from the Naacal. She should, therefore, possess eternal life (immortality).

And yet, if at the end of Chapter 6, the player chooses to return to Tahiti and remain with Harry then the game finishes with Norah’s death.

Why?