Generally, it is form I-94 (which used to be a white paper stapled into the passport and later became an online document), or some stamp in her passport. If she was driven across the border from Canada, things can get more complicated, since there may have been no such document issued to a Canadian citizen. Generally, anyone coming to the U.S. by air will have evidence of lawful inspection and admission into the U.S.
Answered on Sep 13th, 2017 at 6:05 PM