1860 Denton Co. TX
John King, b. TN, 35, farmer
Samuel, b. TX, 1
Rhoda, b. KY, 57
Samuel, b. MO, 16
I can't find John or Rhoda in the 1870 Census. I don't know if they moved or if she died in Denton County.
The Denton County genealogical or historical society has a lot of info & I'd check with them. If she died there, they won't have a death record but they might have her newspaper death notice, inventoried cemeteries and probate records.
You won't be able to search for her prior to her marriage because women prior to 1850 weren't allowed to own property and only show up in marriage and sometimes land purchase records along with their husband's name.