Joni Mitchell Joins Brandi Carlile, Wynonna Judd and More for Surprise Appearance at Newport Folk FestivalJoni Mitchell Joins Brandi Carlile, Wynonna Judd and More for Surprise Appearance at Newport Folk FestivalAllison Russell, Lucius and Marcus Mumford of Mumford & Sons are just a few of the acts who also joined Joni Mitchell on stage.Will GroffWill Groff