I am gonna watch "Hang on Sloopy" on Youtube again. If you do, the dancing girl is Liz Brewer, Rick's girlfriend.
Not trying to turn this thread into an argument, @boxcarman , but a while back ago I watched that video on youtube and then I started doing searches to find out more about the dancing girl, and I did not get the impression that she was his girlfriend. Maybe after the video was made? But I did not get that impression from the youtube interview I saw with her either.