With a honeyed voice and not a drop of guile, Cassidy crafted singular interpretations of even wearily familiar songs. We may have lost this unapologetically uncommercial artist to cancer in 1996 (she was only 33), but her gifts carry on in posthumously released CDs like the winning American Tune. Cassidy's Raitt on time in bluesy bauble ''Drowning in the Sea of Love.'' She simmers in a sultry rendition of ''God Bless the Child.'' And her soulful ''True Colors'' beckons brightly despite its shopworn sentiments. Maybe that's why we love her.