Does Bella (new girl) take the place of Emma in the series...and does Emma return to find Bella as the new "her"?

Yes Emma's leaving and yes Bella's coming into the picture but i think if, and that's a big "if", if there is a season 4 and emma returns i think they can all be friends i don't think Bella will turn out to be bad or just go away cuz shes been a mermaid longer than all three of them, but i don't think Bella's "replacing" Emma she's just another mermaid.

yeah i mean she's blonde and has her the freezing powers.