I believe the blonde was in a cheesy movie (Ultimate Warrior maybe?) that was later screened on MonsterVision, but I can't find the movie in my collection at the moment.
According to its Wiki, at least four mail girls were seen in the show
Briggs was also frequently visited by one of a succession of 'mail girls', including Honey (Honey Michelle Gregory), Reno, Summer (Kathy Shower), and Rusty (Renner St. John), who not only served as attractive, comedic 'sidekicks,' but also brought Briggs fan letters, sometimes from actual prisoners.
Not sure about the movie you mentioned, but Kathy Shower has more credits on IMDB than the other mail girls.