The only Jettie in the 1880 census, who was born in TN, records the following individuals:
Jerrie [Jerry] Marchant, black male age 55
Lizzie, black female age 30 (wife)
Albert, black male age 12 (son)
Henry, black male age 4 (son)
Jettie, black female, age 2 (daughter)
John, black male, age 1 month (son)
Note: On Jerry, I believe that the census taker misspelled his name as "Jerrie" and that the correct spelling is "Jerry." This opinion is based on this: In the Tennessee deaths and burials index, Albert Marchant, born 1868, died 1915, has a father listed as Jerry Marchant, born in NC. His mother's maiden name is listed as Lizzie Fowlkes, born in TN.
I can't be certain it's the same person though. I didn't find an exact birthdate.
That said... Are you sure you didn't misread a record and you're actually looking for Jennie Jenkins?
I located a Jennie Jenkins who was born in Tennessee, and died a few months old. The grave marker says:
Birth: Nov. 7, 1878
Death: Feb. 28, 1879
A.R. & S.E. Jenkins
It is located at Mount Pleasant Methodist Church Cemetery, Lauderdale County, Tennessee, USA. As she was not stillborn, but rather died as a baby, it is possible she was in the other county at the time, rather than in Dyer County. Lauderdale is immediately South of Dyer (they share a border).
Here are the links to the information on Jennie Jenkins:
And a map of the TN counties (Dyer and Lauderdale both on far West side):
The only other variant I could think of is Jessie, and while I found some records for a Jessie Jenkins (white female, born in TN, married to a William Jenkins), I can't be sure since I cannot find an exact birthdate for her.