This Is The Post In Which I Ask For Help

I have begun researching my great-great grandmother Joanna White, wife of Thomas Jefferson White. They lived in Surry county, NC. I grew up hearing about Joanna, our"Irish grandmother". Oral history is vague and included the surnames Lyons and Barrett.  Oral history also tells that Joanna was a widow when she came to America.

 I am intrigued by Joanna.  I have not done immigrant research and am looking forward to learning more about my great great grandmother and this area of research.  My long range goal is to trace Joanna's family back into Ireland.

Joanna Lyons White

b. 25 July 1852

m. 20 Sep 1874

d. 6 Jun 1910

While I held the oral history in the back of my mind, I searched the records for clues to exactly who Joanna was and exactly where did she come from.  Would facts found in the records support the family's oral history?

I started with the traditional records including the census records,  the marriage records and death records.  Right away, what I found caught me off guard.  Joanna (sometimes spelled Jonah) was not born in Ireland.  Census records give three locations for her place of birth: NC, VA, and D.C.  Following Joanna back  through the census records, finds her in the home of William Richard Wilmoth and Joanna Wilmoth in 1860 and 1870.  Joanna Wilmoth (the elder) was born in Ireland.  Later census records show both of Joanna's (the younger) parents were born in Ireland.  WR Wilmoth was born in NC. Because Joanna (the younger) was living in the home of WR Wilmoth, many researchers assumed that she was his daughter.

Here's where the story gets even more interesting.....

I came across the marriage registration for Joanna (the younger) and Thomas J. White in Surry County, NC in 1874.  Immediately, the first thing I noticed was Joanna's name.  She is listed in the marriage registration as Joanna Lyons.  Next, Thomas's parents are correctly listed in the record as Joseph and Temperance White.  Joanna's mother is listed as Joanna Wilmoth.  Joanna's father is listed as Unknown.  WR Wilmoth was still very much alive in 1874 and still married to Joanna's mother, the elder Joanna. It would appear that Joanna may well have been William Richard's step-daughter.  (There are records where the younger Joanna appears as Joanna Wilmoth. Using death records and census records I have been able to confirm that Joanna Lyons and Joanna Wilmoth (the younger) are the same woman.)

And this is the point where I get "stuck".  Where do I go from here?

• Was Lyons Joanna's birth name or was she married prior to Thomas White as some researcher think?  I have not found evidence of a prior marriage in the records.
• The elder Joanna appears to be the immigrating ancestor from Ireland.  I am not sure of her surname before her marriage to WR Wilmoth, though oral history tells of a young widow named Joanna Barrett crossing the Atlantic. She would have come to America before her daughter's birth in Jul 1852. 
• Because one of the possible birth places for the younger Joanna is D.C.,  what type of records might I find pertaining to Irish immigrants in that area. in the early 1850's?  

So....if you are  a cousin or Surry County researcher who knows more of the story, I would really like to hear from you.  If you are a fellow researcher, I'm open to your suggestions.