Hi!
There's a page called repfoto.com where you can find some rock'n'roll photos from all time. They have 6 or 7 photos of Cass. She is on an indoor stage, it seems a concert. The description says it was her at a concert at the Royal Albert Hall of London in octouber 1969. I didn't know she did a concert there, I always thought that after the Caesar's Palace gigs she didn't performed again until she was with Dave Mason in 1970.
Maybe Richard or Owen knows something about it and can help.
Thank you!