Who were Grandma Lou's real parents

One of the first people I learned about as a child was my great, great grandmother Lou.

Grandma Lou lived until she was 101!  

My mother has told me many times about going down to Kentucky every year for the Kentucky Derby & visiting with her Mother's grandmother Lou.

The question I have about my great, great Grandmother is who were her real parents?

I think that Grandma Lou was born Louisa Williams.  

(I found this on her marriage record.)

The first census I was able able to find her on, is the 1880 census.  She is listed as the adopted daughter of Henry & Mollie Dodd.  I don't see any other census record with her maiden name.  

I've read in numerous places that it was common practice for black families to "give away" their children to work.  Is that what happened to her?  

Was adoption common in black families in Kentucky in the 1880's?  If so, where would I begin to find records, if they are even available?  I know most adoption records are sealed, but would she have known who her real parents were?