I only know of the two-volume biography of Keats which Lowell published in 1925. From 1915 through 1917 she edited an annual anthology of imagist poetry, wrote poems herself on Keats, and left her Keats collection (which included letters) to Harvard University when she died, but I hadn't heard of her editing two volumes of Keats's poetry. How did you hear about that? Does anyone know any more?
"Why should we be owls, when we can be Eagles?" (Keats to Reynolds, 3 February 1818)