Under an agreement with USA, citizens from USA may prove their nationality with a passport or other public documents, such as:
- Certified copy of birth certificate/Voter registration card/Naturalization certificate to enter Mexico without a visa showing her passport and the "migration Form for Tourists, Transmigrants, Visiting Businesspersons, or Visiting Consultants", which you can obtain from travel agencies, airlines, or at your point of entry into Mexico.