Basically - there is nothing that suggest that she is an alien, even remains of some sort of an aircraft on her island resemble that of World War 2 bomber or old passenger plane.
Even Neri's abilities are humanly possible - i did some research on the subject and it's known that divers, especially those who train since childhood, like Polinesian pearl divers can get such stamina and endurance. Her talking to whales may be more of hearing ultrasounds whales use for communication and living close to nature. And such people often have ESP [extra sensory perception] abilities too.
It's only her blood work that it's said that is non-human. But that is in the very end of season 1 and it may have been altered when movie guys decided to extend the show and use ideas from X-files like movies.
So - what do you think?
I have tried some of Neri's lifestyle and it got me into thinking that it may be a true story made into a movie script.