Louella is an old old name.
Its the female Lous who AREN'T actually Louellas that's er... new.
I think its also a common MIDDLE name for girls. Again, I think it USED to be "Louella" that way too, but over time became "Cindy Lou", "Mary Lou" (as opposed to Marilu), etc. SOME of whom I bet eventually wound up being nicknamed simply "Lou".