What if the berry Elina ate revealed her true self was destined to be a Sea Pixie/Sea Butterfly? she was destined to belong in both worlds. This means she becomes a fairy on dry land, and a mermaid when in water. These aren't merfairies since they are dwarfed and don't transform. We see the species in the toyline. Mattel could have used this opportunity to explain that species for the toyline better, all abotu marketing. And like the little girl at the beginning of the movie, and I assume a Sea Butterfly is the aquatic offshoot of Mariposa's species. And this way she could be with Nori whenever she wanted! How would you feel about that movie twist?
Here is a slightly annoying commercial https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DFlT5yGwBkXI&psig=AOvVaw37HC_nx_Wv3efO_PHlxUoQ&ust=1755990231596000&source=images&cd=vfe&opi=89978449&ved=0CBoQ3YkBahgKEwjgxbbBw5-PAxUAAAAAHQAAAAAQuwE