At some point prior to 1898, Allison was married off to Terrence O'Dowd.
Events of Red Dead Online
During the mission "Love and Honor", Terrence O'Dowd tasks the players to rescue her, claiming she was kidnapped by outlaws and taken to Twin Rocks. Once the players have dealt with the gang and enter the building that she and Cliff are in, Allison and Cliff plead with the players to leave them be or save them. The players are then given the choice of either helping her and Cliff escape or to killing Cliff and bringing her back to Terrence.
If the players choose to help Allison and Cliff, the players will escort them to their destination while fending off gunmen hired by Terrence.
If the players choose to kill Cliff, the players will kidnap Allison and take her back to Terrence while fending off the remaining members of the gang.
As shown in the few interactions with her, she holds passionate hate for her husband, Terrence O'Dowd, and would much rather be with her lover Cliff. When the players first encounter Allison she is obviously in distress and pleads with the players that she will "not go back" to Terrence.