my sister lives in mexico and gets her non imagrant visa tomorrow, can she come to the US the sane day?

If your sister obtains a nonimmigrant visa tomorrow in Mexico, and it is a B-1 business or B-2 visitor's visa, she can enter the US immediately. If F-1 student, she can only enter within the period of time of 30 days prior to the beginning of schooling. If H-1B, she is allowed entry within the 10 day period prior to the beginning of the H-1B working period.Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.  

If the visa is valid for the travel date in question, she can travel on the visa right away.