A very simple sim I made a long time ago that I am putting up by request.  She is blue in the game but since 4 of the pictures were taken in Spring, she looks greenish.

The mermaid mesh is by marvine and can be found here; it's the blue-gold-green file.  
The skin is Pixie Serpent by Enayla and can be found here
The hair is from Sunair at The Sims Resource mesh T002 here; if it's not still free you can get it here.