With reference to the 1870 Calcasieu Parish LA census and Hebert (Herbert's) Garlington household, there were also four other Calcasieu Parish Garlington households listed under the names of Benjamin Garlington, D.F. (Doctor Frank, I believe?) Garlington, Samuel Garlington and Susan Garlington.
Have you checked to see if any of these four other 1870 Calcasieu Parish Garlington households included a Mary Garlington or Mary J. Garlington?
If they did not, then it would be a pretty good bet that your "Mary J. Garlington" was one in the same person as Hebert(Herbert) Garlington's "Mary (age 23) Garlington" despite the calculated birth year difference of "Abt 1847" (from the 1870 census) and 1850 (from the Thomas Family Bible)
The other question that is in need of an answer is if your Mary J. Garlington married John Lane Burrough on 10 Sep 1868, then what was she doing living in Hebert (Herbert's) household just about two years later when the 1870 census was enumerated?
That question, of course is based on the premise that your "Mary J." is the same person as "Mary (age 23)" who is shown residing in the Hebert (Herbert) household when the 1870 census was enumerated.