Pretty old post, but I thought I'd reply anyway. I've been researching the Overall line for a number of years and have never found any shred of evidence that Jacob Overall was ever married to a Nancy Lawrence of Shenandoah. There are many errors in the old genealogies of Cartmell and Wayland surrounding the Overall family, and this is likely one of them.
Not only is there no evidence of the Nancy Lawrence of Shenandoah, in fact, there is evidence that Jacob Overall Sr married an Elizabeth Hammet in Shenandoah in 1798. Elizabeth moved to TN with Jacob in the early 1800s. In 1815 Jacob posts notice in the Carthage Gazette announcing his separation from Elizabeth. The next month Elizabeth's neighbors post their support for her character also in the Carthage Gazette. Elizabeth goes on to appear as head of household on the tax lists until at least the 1839 tax lists when she either moves, dies, or remarries -- as it is her last appearance in the records that I have found.
Of note, if Elizabeth and Jacob separate in 1815, then heirs Jacob Jr, Israel, Lucinda and Andrew Jackson Overall are likely children of this first union (but birth years are a bit sketchy, so it's hard to tell exactly).
Jacob Sr goes on to have at least 4 more children who survive to adulthood, so he likely maintained another "wife" after Elizabeth, but he would not have been able to formally marry her, as he was still legally married to Elizabeth. So, since he is now in TN, it is possible that this second companion "could" have been from the Lawrence family of the Smith/DeKalb area of TN.
Jacob Sr dies intestate, so if this this new wife survived Jacob Sr, she would likely not have been considered a legal heir and is not mentioned in any further court records that I can find.
Although no longer with Elizabeth, Jacob would have had to provide for her residence and likely a small allowance. She does maintain some dower property that Israel and Jacob Jr must sell after her death (court records contain a power of attorney from Israel to Jacob Jr for this transaction).
As far as the Lewis Lawrence that is involved in the settlement of Jacob Sr's father's estate in the Shenandoah, I do not believe this is the same Lewis Lawrence of Smith Co, TN as is often claimed. Smith Co Lewis Lawrence would have been just barely old enough to legally act in that capacity (perhaps not at all given the uncertainty of his actual birth date) and has no real connection to the Overalls while in VA. Furthermore, records indicate that there is another Lewis Lawrence actually living in the Shenandoah around the time of John Froman Overall's death.
Hope some of this might help you or future researchers.