I know Find a Grave isn't exactly a valid source, but I found this information on her memorial bio that might explain it. Here it is:
I am not sure if you were aware but her parents have been proved not to be Edward and Martha (Miller) Jackson.
Several possible birth locations are offered for Abigail Jackson (1) is Washington Co., PA and (2) Wilkes Co., NC. I have no proof records of either though the DAR accepts the Washington Co. PA location. I've also found the 1880 census of her 71 year old son Stephen which says his mother was born in Georgia. It is possible she was born in NJ as so many charts say; because her father William was born there. But I'm thinking most of those charts say NJ because we know that's where Edward's children were born and early researchers thought she was Edward's daughter. LATER: Also her daughter Martha says her mother was born in Georgia on the 1880 census. So this 1880 Georgia reference is a new area to look for William's marriage and birth of his children.
Conflicting info about Abigail being named Sarah Abigail and a dau of Edward Jackson of Harrison Co., VA has been refuted in the Conflicting Data section of the Jackson website: http://www.jacksonfamilygenealogy.com
Marriage info was taken from image of the actual bond signed by William Jackson and Jonathan Hughes. The date is clearly 11 July 1786. The image is available in the Conflicting Data section of the above web site. (Here is that link: http://www.jacksonfamilygenealogy.com/pages/conflictingSarahandAbig...)
In 1786 William Jackson signs marriage bond for Abigale Jackson to Jonathan Hughes. Jonathan was born in Harrison County (W)VA; he enlisted and served in various locations during the Revolutionary War and after the war, he became an itinerant schoolmaster. He went to Wilkes County, North Carolina in 1783 and married there in 1786 to Abigail Jackson. By 1808 Jonathan and Abigail moved to his home area of Harrison County, Virginia where several of their children were born, raised and married there. Jonathan and Abigail spent time in Ohio and Indiana and in 1835 went back to Harrison County "because I have children who settled there" per his pension application.
As mentioned on our link: http://www.jacksonfamilygenealogy.com/pages/conflictingSarahandAbig... There are three pages that you should view. The DAR is already aware of this conflict. Edward who married Martha Jackson was never known as William. His brother is William.
https://www.findagrave.com/memorial/55441313/abigail-hughes