She and her family survived with him, and created a community in the sewers under Pittsburgh. They expanded throughout the rest of the sewers, and soon grew their community to about fifty people. They even had rain catchers, which Susan regularly monitored. However, the community fell when one survivor left a door open, allowing Infected to flood in. Her husband Kyle became trapped in a room with several children, who killed them out of mercy and committed suicide to avoid being killed by Infected.
Susan, Ish, and several children escaped. Their whereabouts and fates are currently unknown, though Ish left a note saying he had to stay strong for Susan's sake, who presumably was suffering from post traumatic stress disorder.
Events of The Last of Us
Joel, Ellie, Henry and Sam crossed through Susan's community when trying to reach a radio tower. Joel is able to find notes left by Susan and the group, along with facing the Infected that remained from the attack.