You wrote:If there was a document in Edgefield of Lucy I have not seen it...
Remember that just because you haven't seen a document doesn't prove its nonexistence. Lucy is well-documented as having lived in Edgefield after her husband’s death.
In fact, there is still another document (besides the 1809 deed and the 1790 census) showing Lucy (and her son, Paul) in Edgefield Co., to wit:
Lucy Abney & Paul Abney of Edgefield Co. and Ninety Six Dist. sell to Absolom Posey of Union Co., S.C. for 5 shillings, a tract of land in 96 Dist. on Broad River containing 390 acres, part of a tract of 640 acres granted Nathaniel Abney by Benjamin Guerrad, Esq. 20 Jan. 1785, bd. by out limits of two other places of the original tract conveyed unto James Sims and Joshua Martin, with all houses, orchards, fences, gardens, waterways, &c. /s/ Lucy (L) Abney, Paul Abney /w/ Agatha Boulware, Rachel Boulware & Robert Rutherford Boulware
Again, since I lost all my documents in the flood of Hurricane Katrina, I cannot send you a copy. However, it is from Deed Book C, pp. 212-214. As in the 1809 deed, Lucy signed with "her mark". Paul [Collins] ABNEY also signed the deed showing he was part owner of the land. All three witnesses of this deed were near kin to Dorothy “Dolly” RUTHERFORD, wife of Paul Collins ABNEY. This deed serves as proof that this Lucy ABNEY in Edgefield was the widow of Dr. Nathaniel (as she was part owner with their son Paul of his land), and that Paul was their son. I think this more than puts to rest whether or not Lucy was in Edgefield. She obviously was.
You also wrote: Edgefield was where the sons and daughter of George m. Unity resided.
While that is also true, the children of George m. Unity were certainly not the only ABNEY’s in Edgefield. Besides Lucy and son Paul (and younger sons Robert & Nathaniel), “Gentleman” John was there (land grant of 15 Feb 1798). Paul ABNEY m. Eleanor HAMILTON was there (land grant 05 Feb 1798) and he died there 27 Dec 1820.
There are, no doubt, many documents which are waiting to be discovered and countless others which have been discovered but have only been seen by limited numbers of researchers. Through a readiness to share and work with other researchers, and those of other families we can learn much more about our own ancestry. I have always held this belief and a willingness to share. A big lesson here would be just because YOU can’t prove it doesn’t make it less true. Someone else may have the proof. This is why sharing is so important to the proper documentation of one's family.