H20 powers could someone help me solve the mistery ( props)

so the original sirènes louise julia and gracie had the three powers one power for each mermaid then emma cleo and rikki also had one power for each mermaid . and i read that charlotte had the three powers because she was alone in the moonpool
So there are three powers but because there were plus sirènes in the pool the powers had to divisé, split makes sense but what about Bella's power i mean with the original sirènes it makes sense bella wasn't born yet but how is it that charlotte didn't get the fourth power (hope it makes sense )