Events of The Last of Us Part II
At some point, Ellie was assigned Shimmer as her personal horse to ride while on patrol in Wyoming. She was kept in the settlement's stables. Ellie rode her regularly, notably alongside Joel to traverse to a music store to look for guitar strings.
In the winter of 2038, Ellie rode Shimmer to go out scouting along with Dina with her horse, Japan. She rode with her all the way to Eugene Linden's supply station at a library, and stayed there to ride out the storm. Ellie later rode Shimmer to Abby Anderson's hideout while searching for Joel and Tommy.
To travel to Seattle, Ellie and Dina rode Shimmer to and around the city. However, they eventually set off a trap mine that crippled Shimmer, breaking her legs. Ellie was forced to watch as a Washington Liberation Front soldier, Mike, shot Shimmer in the head.