Sharon, The Brockwell lines I have unravelled so far do not include a person even close to your ancestor, Nancy Brockwell.
There is a line of Brockwell families apparently descended from Reverend Charles Brockwell who was sent to the colonies by the Church of England about 1737 - according to information in "Emmigrant Ministers to New England". I believe he eventually became the leader of the Boston Parish.Charles Brockwell - Clergyman - AGBI - Refer to Founders of the Massachusetts Bay Colony, by Sarah Saunders Smith, Washington, DC, 1901 (372pages)
Another "Yankee" Brockwell ventured into Petersburg in 1865: Thomas Brockwell, Private, 10th Vermont Heavy Artillery, Union Army, was killed during the siege of Petersburg, VA, 6 June 1865.He is buried in Poplar Grove National Cemetery, Near Petersburg, VA, Division D, Section A, Grave 61.It is irony that this Yankee Brockwell would be killed during the siege of the largest city in the area where most of the Southern Brockwell's were born.
Some made it to Wisconsin: Jay Van Brockwell, WI enlisted as Union Army, Private, 11/19/1863 Others to Washington State and Oregon and so on.None of those seem to connect to the southern Brockwell families - who seem to originate in Southeastern Virginia.
I have always assumed that the southern Brockwell families were not directly related to Reverend Charles Brockwell, but I keep him on the fringe of my information. I think he may be the ancestor of the thin line of Brockwell families across the northern tier of states.