Donna was much maligned, and rightfully so, for painfully off key wailing at the worst possible moments in the Dead's epic early 70s jams. In fairness, much of that was to do with technical issues on stage with her inability to hear herself. Rumors even exist that some misogyny within the crew contributed to this. But that's here-say so perhaps best unmentioned.
That said, her work within a seminal time of Jerry's solo career, his embarkment of JGB, is top flight. And moreover, duets in '77 with Bobby during the likes of Cassidy and Looks Like Rain are often fantastic. Not to mention the extra charge in the final chorus of some '72 Sing Me Back Home renditions. Make my old memories come alive indeed.
RIP, Donna-Jean.