If my wife is in a 2 year grad school program and taking 2 classes at a time, is this considered full time?

No

It's decided by the school, but I would assume two classes would not be full-time.

Additionally, the program would ask because of the education credits, but since she is in Grad school, the American Opportunity Tax Credit would not be available regardless. You may be eligible for the Lifetime Learning Credit, which has neither requirement. 

Also, she may have a "Savor's Credit" if she is working and has any retirement savings done through her employer. That credit is not available for full-time students.  

Grad students are not eligible for the more generous American Opportunity Credit (AOC) which requires that the student be half time or more.

Grad students are eligible for the Lifetime Learning Credit (LLC) which is a non-refundable credit equal to 20% of tuition and fees paid (up to $10,000). There is no minimum course load.  A single class would qualify.