She's playing a dulcimer on the original 'Blue" cut. James Taylor is playing guitar. Russ Kunkel played on several cuts on the LP, but I don't believe there's any percussion on 'A Case Of You'. Just listened to the cut on 'YouTube' and am 're-amazed' at her vocal dexterity. And how natural and unaffected it seems in comparison to other singers. Celine Dion, Patti LaBelle, Barbara Streisand, etc. all seem to 'use' songs to get their licks in. The only singer I can think of besides Joni Mitchell who always seemed to be well within the boundaries of 'taste' while displaying remarkable technique is Eva Cassidy. Much to our loss she's been gone for over 10 years.