My wife paid for online college in Mexico, is she required to have a 1098T in order to claim College tuitions ?

No.  In order to qualify for an education credit, the school must be eligible to participate in a student aid program run by the U.S. Department of Education. Please review this IRS website for additional requirements. There is also a link in the website to check if the school is eligible for the educational credit.

In a short answer, in this case, a 1098-T needs to be issued to receive the credit. 

Q.  Is she required to have a 1098T in order to claim College tuitions ?

A. Simple answer: no.  Most eligible foreign schools meet the exception rule*.

But, on the other hand, most foreign schools are not eligible institutions. Her education probably does not qualify for an education credit or deduction. 

 To be eligible for the tuition credits or tuition & fees deduction, the course must be taken at an "eligible institution". The school should be able to tell you if it is an eligible educational institution. In general, an eligible educational institution is an accredited college, university, vocational school, or other postsecondary educational institution, including accredited, public, nonprofit, and proprietary (privately-owned, profit-making) postsecondary institutions. Additionally, in order to be an eligible educational institution, the school must be eligible to participate in a student aid program administered by the Department of Education. If they issue a 1098-T they are probably an eligible institution.

Enter your school at the link below, to see if it's on the dept. of education list.

https://fafsa.ed.gov/FAFSA/app/schoolSearch?locale=en_EN (choose foreign country for state)

*

 “However, a taxpayer may claim one of these education
benefits if the student doesn’t receive a Form 1098-T because
the student’s educational institution isn’t required to send a
Form 1098-T to the student under existing rules (for example, if
the student is a nonresident alien, has qualified education
expenses paid entirely with scholarships, or has qualified
education expenses paid under a formal billing arrangement). If a
student’s educational institution isn’t required to provide a Form
1098-T to the student, a taxpayer may claim one of these
education benefits without a Form 1098-T if the taxpayer
otherwise qualifies, can demonstrate that the taxpayer (or a
dependent) was enrolled at an eligible educational institution,
and can substantiate the payment of qualified tuition and related
expenses.”  https://www.irs.gov/pub/irs-pdf/f8917.pdf