I suspect you have solved your riddle by now, but I thought I would comment on some aspects of your 4 prior posts.I have fairly good knowledge of the family of Thomas Elms & Rosanna Hadden Elms, but I have to rely on a short Elms history  for any details about Samuel Elms & Mary Peel Elms's family.
If you have convinced yourself that Eliza (b.c.1842) was not a child of Thomas's (son of Samuel & Mary) first marriage, then I would think that Thomas's 2 older brothers (Garret & James F.) would be the the primary suspects.Thomas's 2nd marriage didn't occur until c.1847.Younger brother, Carson's oldest child was born in 1855.
Interestingly, this Elms history  has listed Elizabeth Elms (b.1826),the youngest daughter of Samuel & Mary, as the Elizabeth who married a Mr. Cable, and died in KY.Based on your research, this account must be incorrect.
Hutchinson, Charles;"Elms Family History",Independence Co. AR, Historical Society Chronical;Apr-Jly, 1991.
I really doubt that your Eliza Elms(b.1842) came from the Thomas & Rosanna Elms branch of the family.Here are some short, thumbnail sketches of the 5 sons:
David M. Elms m.Melinda O'Neal 28 Jul 1842, in Ind. Co.....oldest child was Henry Elms b.3 May 1843.
Hadden Elmsm.Lucy Deadman, __ 1840, .....oldest 2 children were Thomas H. Elms b.1841;and Rosanna V. Elms b.1843.
Samuel Elmsm.Louretta Holand, 23 Mar 1841, in Ind. Co.....oldest child was Harvey Elms b.1843.
Thomas Elmsm.Lucinda O'Neal,20 Jly 1843, in Ind. Co.....oldest child was David M. Elms b.1847.
James Elms........is an enigma ! .....almost no records of him.The Elms history  suggests that James Ellams b.c.1815, and single, in the 1850 census of Izard Co is this James.I suspect, however, that the James Elms b.1825, and married, in the 1850 census of Washington Co TX is the James, son of Thomas & Rosanna.He is several households away from John O'Neal.....and although they are not listed, I believe David M. Elms, Thomas ELms, and other siblings are in Washington Co TX by 1850.The "story" about the O'Neal & Elms listings (or lack thereof) in the 1850 Washington Co TX census is a long one, and probably not appropriate for here.