The tree seems to be an import from Ancestry.com. I looked at a couple of Sarah Gist trees, which seem to be unsourced. One did describe the situation you described. Another, still unsourced, listed only two sons, and reported this: "Death: 1837 • Monroe co, Kentucky. [She] was micajah's first wife.....died after 2nd child...all this happened withen a 2/3 yr period & micajah remarried in 1839 in Monroe co ken. to mary p. glidewell....sarah's marriage to micajah may have been by indian law" So it could be that attaching the birth of Narcissa to Sarah is incorrect. Even if she died in 1837, did she die in Kentucky, or in Texas? Without finding source material, anyone's guess is good as another. Although if the remarriage of micajah in 1839 can be affirmed, that would give credence to the belief that Sarah was not the 1841 mother of Narcissa.