Drats!

Anyway, she was the one to sing Science Fiction Double Feature in the OG stage show. In the screenshots provided, she is played by Patricia Quinn, better known as portraying Magenta in the movie. She sang the songs with much more energy than the lips. She is also usually double cast with Magenta's actress.

As Brian Thomson, her original concept man said to me, she was born when him and Jim Sharman went to a single screen theater showing of Cabaret. There were many things before the movie, and during intermission, this girl, dressed in pink to sell ice cream and that sort of thing came to the front of the theater and stood there, smiling, waiting for someone to buy something from her. Nobody did.

The usherette was then born. I suggest the OG London cast recording of Science Fiction Double Feature and Reprise to really get a feel for Pat Quinn's portrayal.