Papers on Literature and Art
p73“The life of Bach which I have before me, (translated from the German of J. N. Forkel, author also of the "Complete History of Music,") is by far the best of any of these records.”
The same sentence also names A Complete History of Music. Counted as one engagement.
Fuller, Margaret. Papers on Literature and Art. New York: Wiley and Putnam, 1846.
Fuller explicitly identifies this as her source for Bach and rates it 'by far the best of any of these records.' She quotes from it extensively throughout the Bach section.