Mary Elizabeth Jenkins was born to Archibald and Elizabeth Anne (nee Webster) Jenkins on a tobacco plantation near the southern Maryland town of Waterloo (now known as Clinton). Sources differ as to whether she was born in 1820 or 1823. There is uncertainty as to the month as well, but most sources say May.
Conspiracy
Louis J. Weichmann moved into Surratt's boarding house on November 1, 1864. On December 23, 1864, Dr. Samuel Mudd introduced John Surratt, Jr. to John Wilkes Booth. Booth recruited John Jr. into his conspiracy to kidnap Lincoln. Confederate agents began frequenting the boarding house. Booth visited the boarding house many times over the next few months, sometimes at Mary's request.  George Atzerodt and Lewis Powell boarded at the townhouse for short periods. Atzerodt, a friend of both John Jr. and Booth and a co-conspirator in the plot  to kidnap Lincoln, visited the boarding house several times in the first two months of 1865. He stayed at the Surratt boarding house in February 1865 (for one night or several, sources differ), but he proved to be a heavy drinker, and Surratt evicted him after just a few days.  He continued to visit the townhouse frequently afterward, however. Powell posed as a Baptist preacher and stayed at the boarding house for three days in March 1865. David Herold also called at the home several times.  As part of the plot to kidnap Lincoln in March 1865, John, Atzerodt, and Herold hid two Spencer carbines, ammunition, and some other supplies at the Surratt tavern in Surrattsville. On April 11, Mary Surratt rented a carriage and drove to the Surratt tavern. She said that she made the trip to collect a debt owed her by a former neighbor. However, according to her tenant, John Lloyd, Surratt told him to get the "shooting irons" ready to be picked up. On April 14, Surratt said that she would once again visit the family tavern in Surrattsville to collect a debt. Shortly before she left the city, Booth visited the boarding house and spoke privately with her. He gave her a package, later found to contain binoculars, for Lloyd to pick up later that evening. Surratt did so and, according to Lloyd, again told Lloyd to have the "shooting irons" ready for pickup and handed him a wrapped package from Booth. (Booth and Herold would pick up the rifles and binoculars that evening, as they fled the city after Lincoln's assassination.) Lloyd repaired a broken spring on Surratt's wagon before she left.

Q: What conspiracy was she involved in
A: conspiracy to kidnap Lincoln.
Did she have co-conspirators
Confederate agents began frequenting the boarding house. Booth visited the boarding house many times over the next few months, sometimes at Mary's request.
Confederate agents began frequenting the boarding house. Booth visited the boarding house many times over the next few months, sometimes at Mary's request.