I wonder if the original film mentioned was early 1930s. I think Joan went brunette fairly early on in her career.
A friend loaned me his DVD of SUSPIRIA which I have never seen all the way through. It was Joan's last feature film. Her final appearance before the cameras, so far as I am aware, was "This House Possessed," a 1983 TV film with Parker Stevenson. It was a real shock to see Joan playing a half-mad bag lady wheeling a shopping cart around town in that one.
Best, G.