There's a note to the name "Dinah" HERE, which says: "Dinah was a slang term for a slave woman and, by extension, any woman of African-American descent, as in the song lyric 'Someone's in the kitchen with Dinah, Someone's in the kitchen, I know.'"

James J. Fuld writes in The Book of World-Famous Music, 4th ed. (Dover, 1996, p. 309): "The first known appearance in print of I've Been Working on the Railroad is under the title Levee Song, in Carmina Princetonia (8th ed., Martin R. Dennis & Co., Newark, N.J., 1894), p. 24." This version doesn't have the "Someone's in the Kitchen" part. It would be interesting to quote the whole song, from my copy of Carmina Princetonia: The Princeton Song Book, 21th ed. (G Shirmer, 1927, pp. 70-71).

LEVEE SONG
(copyright, 1894, by Martin R. Dennis & Co.)

1.
(SOLO) I once did know a girl named Grace--
(QUARTET) I'm wukkin' on de levee;
SOLO) She done brung me to dis sad disgrace
(QUARTET) O' wukkin' on de levee.

Chorus:
I been wukkin' on de railroad
All de livelong day,
I been wukkin' on de railroad
Ter pass de time away.
Doan' yuh hyah de whistle blowin'?
Ris up, so uhly in de mawn;
Doan' yuh hyah de cap'n shouin',
"Dinah, blow yo' hawn?"

2.
Sing a song o' the city;
Roll dat cotton bale;
Niggah aint half so happy
As when he's out o' jail
Norfolk foh its oystahshells,
Boston foh its beans,
Chahleston foh its rice an' cawn,
But foh niggahs New Awleens.

~Masato