Aelf can mean elf, but also simply supernatural, which might well, in the Christianized Anglo-Saxon wold, have a gloss of heavenly. (In all those Edwards and Edgars etc, the word 'Ead' means blessed.)
It should be noted that Elfleda can also be a variant of the Anglo-Saxon feminine name Ælfflæd, which consists of the Old English elements 'ælf' meaning "elf" and 'flæd' meaning "beauty". An example of this is the 8th-century saint Ælfflæd of Whitby, whose name is also recorded as Elflaeda and Elfleda.- https://en.wikipedia.org/wiki/%C3%86lffl%C3%A6d_of_Whitby (in English) - see the entry for Ælfflæd on page 17 of "Women's Names in Old English" written by Dr. Elisabeth Okasha: https://books.google.nl/books?id=3z0-fUT70DsC&pg=PA17 (in English). [noted -ed]