From NetComics:

Abandoned in a cabbage patch as a baby, Iseulbi [aka Misty-Rain] is saved from certain death by a witch who brings her up as her own. Far from the company of humans, she is raised as one of the Dokebi, a magical race from Korean myth. Among them she is happy and content, until one day she loses the trust of her protector, causing the enchantment that had kept the secret of her true identity to be broken. She is cast out to the world of her birth and must find her place among her own kind.

A mixture of off-the-wall family comedy and bittersweet love story, For the Mermaid Princess is the story of a girl with a gentle manhwaga father, a whip-wielding nutjob of a mother, and four older sisters.
When her family moves to a new house, Lee Suelbi discovers just how difficult it can be to balance family, friendships, and love.