是说如果从墨西哥入境的话，那她就不需要美国签证，只要她在2月18和3月18日之间入境美国？
-Correct she can use the benefit of visa automatic revalitation rule to reenter US with her I-94 if she reenter from Mexico within one month from the date she leaves US and before the I-94 expires.
See:
http://travel.state.gov/visa/temp/info/info_1299.html
