回複：謝謝。不過不太明白，可以再請教一下嗎

是說如果從墨西哥入境的話，那她就不需要美國簽證，隻要她在2月18和3月18日之間入境美國？

-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