My sister in law is flying LGA-ORD-MEX. she is not a U.S. Citizen nor resident. She is visiting us from SIN before a conference in MEX. does she clear immigration at LGA or ORD? Trying to make sure her flight allows enough time. She's flying UA. Also on the return it is MEX-IAH-LGA. Pretty sure everything is done at IAH like any other international-domestic connection, but forest me if I'm wrong. Thanks!