What kind of relationship do you plan to have with Nalani?

Whatever she decides. I have no immediate plans to play Nalani or mermaids in general, so it is in her own responsibility to write herself into my story.

My first sim will probably try to get a lot of photos of any mermaid but ignore Nalan in her human state, taking her for just another local.
While the family I'm going to send afterwards consists of goofballs who might try to steal a scale, throw a fishing rod after her or snag a strand of hair for good luck.