The director had directed Porn in the 70's without the studio knowing it. He decided to change the actress because of her breast size and her last name was a happy coincidence.
Fun fact: the original girl for that role was cast in the next F13 film. Part 6 is known to show no nudity at all. They asked her if she would and she said its not in my contract so she didn't. She would've in part 6. She was the girl in the winnebago.
Watch Crystal Lake Memories and it explains it all.