Forgive me if I make suggestions you've already tried.Since Sarah shows different birth locations for her father, it sounds like he might have died when she was young, and she heard stories about where he was born and where he grew up, and didn't remember which was actual birth location.
"Republic of Texas: Poll Lists for 1846", compiled by Marion Day Mullins, shows a William Ward in Navarro Co, TX.There's also a John Ward listed, too.
Have you checked probate records for Navarro Co, TX?See if a Ward probate mentions Sarah as an heir?Or, guardianship records.Yes, even if the mother was living, if their was an estate, the court would appoint a guardian for minor children.Guardians did not physically take the children, just reported to the court if any of the estate was sold etc.This was to protect minors until they reached their majority.
Check land records for William Ward, when was land sold?Another place where names of heirs might appear, as they might have had to sign off for final sale of land.And, if minor children were involved the guardian would do it, but the children "should" be named.
Since there was a William Ward in Navarro Co, TX in 1846 check 1850 census to see what info is given.Then follow up with 1860, see if he has a baby daughter named Sarah.If not, then check out the John Ward that was there in 1846, too.
Have you found a Navarro Co, TX history?The William and John Ward being there fairly early, might at least bementioned.Maybe enough info to tell whether they are your line, or not yours.Ward is fairly common, but they might be kin of some kind.
Have you had a chance to post your query on both the Navarro Co, TX GenWeb and GenForum sites?By the way, your query is very good.Very clear and easy to read, with lots of helpful information. Happy Hunting.