Putri Duyung & 100 Kebaikan

Indonesian sinetron Putri Duyung & 100 Kebaikan (Putri the Mermaid & 100 Good Deeds) opens with some familiar fairytale conventions with a young girl named Putri (Jessica Anastasya) who is bullied by her stepmother Lastri and stepsisters Ratna and Ratih. Putri's father is alive and lives with them, but he doesn't notice that Putri is being tormented by her stepfamily.

Putri encounters a talking fish in a pond, but what should be a stroke of good fortune goes badly when Putri is careless and breaks her promise to return the fish safely. Putri is cursed into becoming a mermaid, where scales and a tail will be revealed whenever she's splashed with water. The mermaid queen (Firrina Sinatrya) gives Putri a magical necklace that can turn her invisible and tells her that if she does a hundred good deeds, the curse will be broken. But the later episodes take a turn by doing away with the family drama entirely, and Putri spends most her time being rescued from various villains by her friends. Putri ultimately breaks the curse by skipping the rest of the required good deeds by defeating the Lord of Evil.

This is a simple family story with slapstick and melodrama, and it feels like it's based on a specific story or folkore retelling, though I'm not sure what that story is called. Info would be most welcome! The tails are basic and the "underwater" scenes are simple composit scenes because they're not the point of the story.