In 2001, Haines became a legal officer at the Hague Conference on Private International Law.[15] In 2002, she became a law clerk for United States Court of Appeals for the Sixth Circuit Judge Danny Julian Boggs.[16] From 2003 until 2006, Haines worked in the Office of the Legal Adviser of the Department of State, first in the Office of Treaty Affairs and then in the Office of Political Military Affairs.[17] From 2007 until 2008, Haines worked for the United States Senate Committee on Foreign Relations as Deputy Chief Counsel for the Majority Senate Democrats (under then-chairman Joe Biden).[18] She then worked for the State Department as the assistant legal adviser for treaty affairs from 2008 to 2010.[19]