Unless she's changed recently, I don't recall Joan Baez being into special tunings (anything other than the standard E A D G B E). My guess would be that she had put new stings on her guitar not too long before the concert and had to keep adjusting them. Also, she uses a capo from time to time, and often when you put a capo on or move it from one position to another, you have to fine-tune a string or two. Another possibility might be a bit of nervousness if she was having vocal problems, like a cold or something like that.

I havent't seen her recently, but I wonder if she still plays that beautiful 1929 Martin 0-45. Great instrument for song accompaniment!

Don Firth