Hi Deli, I love your little mermaid idea. I am new here, so this may not be what you are expecting, but here goes:
How did the girl become half-mermaid? Is there a side story to weave into the plot describing how her father met her mother Ė And what happened to the father when he discovered her secret?
What are the professorís motives? Being a marine biologist, one suspects he would want to examine a mermaid close up and be the first to write a technical report. But, could it be that he took marine biology in the first place because he was fascinated by mermaids as a child?
Or does she become the sex-slave of the jealously protective college professor/ scientist determined to breed a new race of marine beings? In which case, could there be irony in a male student or previously rejected boyfriend rescuing her from his clutches?
Lots of fascinating options here.