This is actually from a mainstream porn film in the early 80's "WPINK TV"
https://www.iafd.com/title.rme/title=wpink+tv/year=1984/wpink-tv.htm
In the last orgy scene a girl comes out of no where with Marc Wallace. As the story goes, she was a make-up artist who had just started dating Marc and he convinced her to join him in the scene. It was completely unscripted and they didn't even list her in the credits as a star or a make-up artist. This all kinda came out when they did the re-release of the movie on DVD and they had a sort of an anniversary round table of a few of the stars including Christy Canyon talking about making the movie as a DVD bonus. At one point they briefly mention the jist of what happened but wouldn't say her name and were looking around with a I don't know how much of this we can actually talk about kinda thing at which point they moved on to a different topic.
She later went under various names and other than doing a short hardcore scene with Peter North in "Shape up for Sensational Sex" she made quite a few appearances in softcore gigs as well as over 100 softcore bondage and wrestling video's over the next 20 years. Her more mainstream softcore name was Jasae but she had a few others
https://www.iafd.com/person.rme/perfid=edimedici/gender=f/elise-di-medici.htm
https://www.imdb.com/name/nm0195262/
That's the best story I know of for this kinda thing.