My 6 year old tho is she is a mermaid. When does species transition therapy start? I want to see how she will look with a tail
Unless she's obsessed with this, I wouldn't get too upset. It sounds to me like normal childhood role play. Every little girl in my neighborhood growing up went through the "Snow White" phase, the "Mary Poppins" phase and a few other phases influenced by pop culture. We boys did the same thing, with the "Daniel Boone" phase, the "G.I. Joe" phase, etc.
Don't discourage her from fantasy time. It usually does no harm, and it sure beats the heck out of Ritalin and the other poisons that the drug companies and the FDA are shoving down our collective throats.