The Last Mermaid is one of the carnival freaks. The game's data files list her name as Courtney, but since she has no lines of dialogue, she has no voice actor.
Courtney is a beautiful, blonde woman with a fish's tail. She is topless with only starfish covering her breasts. Being a mermaid, she doesn't speak. She mainly floats in her tank watching the visitors, occasionally swimming around. The "kiss" icon appears when targeted, however, she is out of Jimmy's range and cannot be kissed.
Presumably, the carnival staff picked the name Courtney for her.
If Courtney is added to free roam via hex editing, she walks around on her tail which functions like a pair of legs.