Can I apply for a green card or visa for my grandmother who lives in Mexico?

No. A U. S. Citizen 'cannot' petition a grandmother for a family based immediate relative visa. Furthermore, without further information, it seems possible that she is likely to become a public charge upon her arrival. If this is a parent of a your living mother or father, who happen to be a U. S. Citizen, then there is hope. As a result, I strongly recommend an appointment with a competent and experienced immigration attorney, who can take enough time to investigate and provide reliable legal advice.