Passport questions.. travel to Mexico?

My wife has a green card, a California I.D. and a passport from the Philippines.

Can she / or does she need a U.S. passport to travel to Mexico?

Can she get a U.S. Passport?

What are the requirements in this situation?

you have to be a US citizen to have a US passport. She can go to mexico with her own passport.

If she flies to and from Mexico she must use her Philippine passport, if she travels by land r sea, no passport needed until June 2009. As other answerer said, only American citizens may have an American passport. See site below and read paragraph on "International Travel."