One of the favorite animated Disney heroines of the modern era makes her first 3-D appearance in tonight’s new episode. It’s Ariel, the scaly star of A Little Mermaid, as embodied by JoAnna Garcia Swisher, who once played Cheyenne on Reba McEntire’s sitcom Reba. And who plays evil Ursula? Let’s put it this way. The tentacles may be new, but the face is familiar…