To me, valley girl was a vapid, airhead kind of speaking. This vocal fry has more of a snooty elitist kind of feeling. I don’t hang around teenage girls, so I’m not sure what a group of them sounds like, to better refine my opinion.
I agree, they don't sound alike at all to me. Vocal fry has this gravely thing in the throat going on. Chelsea Clinton talks with vocal fry in her voice.