Harriot was arrested by the NCR government for several murders and was sentenced to a long, if not infinite prison sentence. As a result, she jumped at the chance to join the NCR's people in Project Cook and moved out to Denver.
During the events of Brothers in Binds, she struggled with addiction, that she still hadn't fully recovered from, by the events of Godless America but had gotten out of the 28 day danger period. It was through the support of George McGill and eventually Wilkes Walker, that she achieved this.
After defeating Casimir and the The Copper Toes, she and the other members of Project Cook looked forward to a long life, in an abandoned Vault. That was until Daniel Starling posessed George McGill's body and left, which was the first step in his plan to conquer the west coast with his army of clones and lobotomites.
After defeating him, both she and Wilkes moved to Kentucky, where they lived a peaceful but rather mundane existence. As a result, Harriot contacted Agent Miller behind his back and got them signed onto his mission, to kill Shrike.
Brothers in Binds
Legends of the Wastes