Disney Pixar just released called Luca on Disney plus it's about sea monsters going to the land surface. When sea monsters or merpeople travel to the surface they are magically transformed into humans unless they get wet. So far the only female that able to transform in the movie I guess it's the merboy's mother below the surface I don't know if there's any more female transformation, somebody have to watch the movie and see. Here's a clip from the movie
https://youtu.be/hg0RMhxvPXA