I've been puzzling about something arising from Karen O'Brien's biography, "Shadows and Light". At least twice Karen mentions the fact that polio left Joni with a deficiency in her left side which meant she was unable to master a "Cotten picking" style of guitar playing. While I can see that a weakness of the right hand could lead to difficulty in this respect I can't see why a problem with the left hand would lead to her "ending up playing mostly the 6th string, banging it into the 5th." Looking at early footage of Joni's playing she seems to use a highly developed finger picking style, although it's true this was later abandoned. The development of her many tunings as the result of left hand weakness I can understand as they make for more comfortable fingering on the whole, although more barring which takes quite a lot of strength.
Comments welcome, Jacky