OK, Nieve more closely resembles a sprite or pixie, but a little artistic latitude can be afforded for a good cause
During her evening bath Nieve is usually stubbornly obstructionist about letting us rinse the shampoo out of her hair. She's fine with wetting and scrubbing but her fear of suds in the eyes, and dislike for having her ears submerged in water make it a fight to rid her hair of shampoo.
Nieve's still a little nervous about the water near her ears...
One trick that does seem to work, however, is to tell Nieve that she has "mermaid hair" when she lies on her back in the tub. I think she's read the story of Ariel one too many times. It comes as no surprise that tapping into Disney's magic as a powerful motivator is especially effective on style-conscious children like Nieve.
... but I suppose the praise went too far... now she's showing off
Yes, I'm manipulating her (to her own benefit, I argue), but she is so pleased to hear, "Nieve, wow! Your hair! It's flowing gently from side to side, like a mermaid!" that I feel a bit less guilty about it. And to be fair, if mermaids were to exist, I imagine their hair might look similar to Nieve's when she's bathing in the tub.