(Usually cast in the singing but non-speaking role of "Donna.")
Donna Loren – an intriguing character whose competencies go way beyond just singing and acting – appeared in four of the Beach Party movies. She briefly appears in a duet in one and does substantive solos in three others. Two of these were dance numbers, the other a ballad. Unlike Annette and Frankie, she wasn’t initially cast because of her film experience (these movies were her first) but rather as part of a product placement deal AIP made with the Dr Pepper soft drink company, whom she was a "spokesmodel" for. AIP wanted Donna – she was young, beautiful and could sing like an angel with her strong, confident alto -- and Dr Pepper agreed to "loan" Loren and invest in producing the series…just as long as everyone in the movies were continually shown drinking a particular brand of soda.
Regarding that role, Donna’s contract with Dr Pepper (a conservative, Texas-based company) clearly stated that as a representative of the firm she could not do, much less wear anything provocative (similar to the “urban legend” about Annette’s contract). However, unlike Annette, Donna was 100% in compliance, she never wears a bikini in any of the films, is never seen doing anything more provocative than comparatively docile dancing and yes, her navel is never visible.
The full Loren story
Donna never played a "biker chick" in these films, but she poses as one (with a "Ratz" jacket worn backwards, so the logo wo will face forward) in this rare 1964 AIP publicty shot