There is a John Armstrong who appears on the tax rolls of Christian Co. in 1810, the same year Francis Whiteside appears.  However, this John Armstrong remains on the rolls continuously through at least 1823 (the latest year I have), so I don't see how he could be the same man, unless his widow continued to live there and be taxed under her husband's name.  Also, his land was on the Tradewater River, and the rest of the family lived on the West Fork of the Red River.

1.  James Taylor Killebrew.  1987.  County Court Order Book "B" Part 2 for Christian County, Kentucky, for the years Nov. 1809 - 6 June 1814 for a County Court held at Town of Hopkinsville.  Christian County Family and History Research Society (4465 Cadiz Rd., Hopkinsville, KY 42240). Number in first column is the page number in Killebrew; number in the second column is the page number in Court Order Book B.

p.	p.	Date	Motions
136- 137	359	1 Nov 1813	The last will and testament of John Armstrong deceased was this day exhibited in Court and proved by the oaths of Isaac Clark, [p. 137] and Francis Whiteside subscribing witnesses thereto and ordered to be recorded and on motion of James Whiteside the executor named in said will, who made oath thereto (he being released by the will from giving bond security) certificate is granted him for obtaining letters of administration on the estate of said decedent in due form.
137	359	1 Nov 1813	Ordered that Henry Clark, Isaac Clark, Simon French, Uriah Hatcher or any three of them being sworn before a magistrate do appraise the personal estate and slaves if any of John Armstrong deceased and report.

I presume John Armstrong is Susannah's husband, though there hardly seems time for her to have married twice by 1813 .  Susannah's brother, James, seems a little young, too (he's supposedly only 19), for such responsibility as being executor of a will, but I don't know who else this James could be.  I wonder if we have the birthdates correct for James and Susannah?  Isaac Clark could be Susannah's uncle or one of several cousins of that name.  Simon French is Susannah's second cousin.  It doesn't say whether Henry Clark is junior or senior — Henry Clark, Sr., is Susannah's grandfather; Henry Clark, Jr., is her uncle.   I don't know who Uriah Hatcher is.