The competition produced some lovely responses, from Mudcatters and others (mostly posting directly to my site) and my winners, as announced at Salut! Live today, are

Tasha, Diane Easby, Es Chorlton and Ed Grummitt, who will each receive a copy of the Fotheringay 2 album. They can let me have postal addresses by PM.

Diane remembered being forced to think again, when just about to sing a Sandy Denny song at Les Cousins and spotting her coming down the stairs.
Es Chorlton had a great tale of Fotheringay's response to demands for Banks of the Nile at a Manchester concert.
Ed wrote about a contender for Sandy's greatest gig (the Howff in London in 1973) and Tasha had a delightful childhood memory of thinking Sandy must be a fairy because her voice sounded so magical.

Thanks to all - and to Joe for permitting me to alert fellow Mudcatters.