Overall this is a very beautiful work with nice and calm colours. I like how you made this blurred foreground to create the illusion of depth. The soft pink colours in the tail and her skin match wonderful to the blue tones of background and water. The background is a very nice composition.
What I have to criticize is that the pearls in her hair are much sharper than the hair, this way you can see they are pasted on the hair. Maybe a little blur would do a big job at this point. And maybe you should try to use a hair brush next time you do a work with a cut out model, this helps to cover the cutting edges
I'm very sorry it took me so long to write this critique. Hope you don't mind