Did Erin Moran(Joanie) ever make guest appearances on CIC? I know it was said that her and Scott dated for a while during happy days. Then she had a big falling out with all the happy days stars and tried to make amends a few years later.

No, I don't think so.. they really only dated a few months. She didn't speak to some of the cast members for years after the show ended, she only made amends in the mid 90's or so.