Gracie was born 5 months prior to the war between the Militia and the Saviors. It's unknown what became of her mother but her father is known to have survived long enough to be able to take care of her for those 5 months.
Gracie's father is killed after a scuffle with Rick Grimes. Rick enters her room expecting to see guns but instead finds her. He then breaks down in tears knowing he just left her without a father as well as began to think what would happen to Judith, his daughter, should he meet his death.
After the outpost is cleared out, Rick brings Gracie outside to the other Alexandrians. He suggests that he can bring Gracie home but Aaron steps in, stating that he can take her to the Hilltop Colony where she will be safe.
When the heartbroken Aaron is greeted by Maggie at the Hilltop, she sees that he is carrying Gracie in his arms.
When confronted by Carl outside of Alexandria, Negan references Gracie and wonders out loud what happened to her. Carl doesn't answer Negan about Gracie's fate.