Wife of John Marston and mother of Jack, Abigail was originally a prostitute that accompanied Dutch Van der Linde's gang; she eventually married John and gave birth to an unnamed daughter, who was either stillborn or died shortly after birth, and Jack. After the event that caused John to leave the band of outlaws, Abigail, John, and Jack settled on a small ranch and attempted to lead a normal, honest life. Abigail and Jack were taken by Edgar Ross and his organization to ensure the "assistance" of John Marston in the apprehensions or slayings of his old gang. Abigail says that she and Jack were treated well during their time as hostages, but one agent did attempt to either molest or rape her; however, Abigail claims that she took care of that herself. After the betrayal of Edgar Ross and the murders of John and Uncle, Abigail and Jack returned to the ranch. Abigail only survived her husband by three years; the cause of her death is unknown but it is hinted she died of tuberculosis.
Source: Wikipedia, "List of characters in Red Dead Redemption", available under the CC-BY-SA License.