I call shenanigans!
Webb was born in '78. Slumber Party Massacre came out in '82. Unless she magically grew up in 4 years and stayed the same age, it's not true.
Kinda what came to my mind when I read it, I thought she was a might young to have been in that movie. I wasn't sure what year she was born, but it'd be a safe bet it wasn't the early to mid 60's which she would have had to if she was in SPM.