Traveling to Mexico immigration documents needed

I was told Princess when I booked my cruise with Princess from Los Angeles (San Pedro) to Ensenada that my wife was fine traveling with just her Resident Alien Card (green card). I have since read in a couple of places that a Passport is required of everyone, even a person such as my wife.... a citizen of Mexico but who has a permanent residence card.

Has anyone out there traveled on Princess to Mexico under the same circumstances?

Thanks.

John

Have you read this:

https://help.cbp.gov/app/answers/detail/a_id/1139/~/documents-needed-to-take-a-cruise