Mary A. Banks
Born: 2 March 1837, Jones Co. NC
F: John Mercer, b. Jones Co. NC
M: Polly Amyett, b. Jones Co. NC
Widow: Benjamin F. Banks
Died: 1 March 1919, New Bern, Craven, NC
Buried: Beaver Dam, Pollicksvill, Township, 2 March 1919
Source: NC Deaths
That's all that I found for Mary Polly Amyett Mercer.
I'd look for her and John's marriage document. Their parents might be on it. If not, I'd look for the newspaper announcement of their marrigae which might mention other family members.
I'd contact the genealogical or historical society in Jones County, NC about her death. Ask if they have a local death index, indexed newspaper death notices and cemetery inventories. Other family members might be in her newspaper death notice.
I'd also post the query in the North Carolina, Jones County Message Board. The theory is that someone local to the area will be able to answer your query or tell you which local organization to contact. Successful Searchng!