Emmylou is much, much better than Emmaleigh. But then again, there are no circumstances under which I would endorse the use of Emmaleigh.
I'm sure you've thought of this, but there's a whole world to be explored of lovely names that feature "em" without beginning with it, which, combined with
Lucille, could provide an arguable source for Emmylou (one I like is
Clementine).
--
Sarah