Yes. A mermaid can only lose her powers permanantly if she is in the Moon Pool when the planets all line up with the full moon. This happens once every fifty years. The last episode Emma was in, season 2 finale, this specail full moon occured. Emma wasn't in the water. The pushed charlotte in, and she Nawawala her powers, just like her grandmother, Gracie. Emma couldn't have Nawawala her powers. She is just traveling.
I think she is still a mermaid because i think she's supposed to be in season 4 and there is also gonna be a merman and i also know that in the last episode of season 3 called the GRADUATION Bella, Cleo, Emma, Rikki and Lewis all come back
